If your iPhone 18 Pro keeps restarting (black screen, then the Apple logo), the most common cause is an iOS 27 bug tied to Face ID, which Apple acknowledged and fixed in iOS 27.0.1. So install the latest version of iOS before you try anything else. If the restarts continue after the update, open the iPhone’s panic-full files: what they say tells you whether you are dealing with a software crash or with a sensor or flex cable that has stopped responding.
Quick fix
- Go to Settings > General > Software Update and install iOS 27.0.1 or any later version.
- Until then, if a Face ID prompt fails inside an app (Passwords, a Safari private tab, Apple Pay), enter your passcode instead of retrying Face ID.
- If the iPhone still restarts on the latest version, copy the text of the most recent panic-full files (Settings > Privacy & Security > Analytics & Improvements > Analytics Data).
- If the same message keeps coming back, especially “Missing sensor(s)”, book a replacement appointment and bring the logs.
How to recognize the problem
Reports from iPhone 18 Pro and iPhone 18 Pro Max owners look alike. The screen freezes, touch stops responding for a few seconds, then the display goes dark. The Apple logo appears and the iPhone comes back to the Lock Screen asking for the passcode. Some crashes follow a failed Face ID attempt in a protected app, others happen with no obvious trigger, while browsing or charging. In the worst cases the iPhone gets stuck in a loop: Apple logo, black screen, Apple logo.
One clue confirms a real crash rather than a dead battery: after each restart, a new panic-full file shows up in Analytics Data.
Why does my iPhone 18 Pro keep restarting?
Short answer: in most reported cases, because of an iOS 27 bug in the way Face ID failures are handled, specific to the iPhone 18 Pro and Pro Max.
This kind of restart has a name: a kernel panic. The kernel is the layer of iOS that talks directly to the hardware. When an app crashes, iOS closes it. When the kernel itself runs into a situation it did not expect, its only safe way out is to restart everything and write a report: the panic-full file.
On the iPhone 18 Pro, Apple moved the Face ID infrared camera under the display, next to the clock, while the dot projector stays in the Dynamic Island. 9to5Mac reproduced the bug on a European iPhone 18 Pro. All it takes is opening an app protected by Face ID, covering your face to force a failure, then tapping the button that retries recognition. The phone freezes and restarts a few seconds later. Unlocking from the Lock Screen is not affected. If Face ID simply refuses to work, without any restart, that is a different problem, covered in our guide to Face ID not working on iPhone 18 Pro.
The link with the new Face ID layout is a theory from the tech press, not an explanation from Apple. What is confirmed is that the defect is software: Apple fixed it with an update, with no replacement program.
What exactly does iOS 27.0.1 fix?
Short answer: restarts on the iPhone 18 Pro and Pro Max caused by a Face ID failure, and nothing else as far as restarts go.
The release notes list three fixes. The first reads: “iPhone 18 Pro and iPhone 18 Pro Max may unexpectedly restart when Face ID fails to authenticate.” The other two address a color artifact in some photos taken at 2x at f/1.48 on a small number of iPhone 18 Pro units, and a touchscreen that stopped responding when Notification Center and Control Center were opened at the same time.
That touch freeze affects every iPhone running iOS 27. It does not restart the device, but the way out is a force restart, which is why the two problems get mixed up. We cover this bug and other interface slowdowns in our article on an iPhone 18 Pro that lags on iOS 27.
iPhone 18 Pro keeps restarting after the update: is iOS 27.0.1 enough?
Short answer: yes if your crashes came from the Face ID bug, no if the cause lies elsewhere.
In South Korea, the press reported around 1,500 iPhone 18 Pro units exchanged for these restarts in the first days of sales, a figure attributed to Apple. The company said there that the Face ID issue had been resolved and that other defects would go through regular customer support.
The test is simple: a few days of normal use on the latest version of iOS. No new panic-full file, case closed. New files, read them.
How do I read iPhone panic-full logs?
Where to find them
Open Settings > Privacy & Security > Analytics & Improvements > Analytics Data. The list is sorted alphabetically: scroll down to the letter P. File names follow the pattern panic-full-YYYY-MM-DD-HHMMSS.ips, with the date and time of the crash. Shorter panic-base files may also appear.
If the list is empty, go back one screen, turn on Share iPhone Analytics, then check the list again after the next restart.
What to look for
Tap a file and a dense block of text appears. Only one line matters: the one containing panicString or starting with panic(cpu. The Share button lets you send it to Notes or by email. Compare two or three recent files: an identical message from one crash to the next is worth far more than a single file.
The most common messages
“userspace watchdog timeout: no successful checkins from…”: the system watchdog expects regular check-ins from certain services. When one of them stays silent for about 180 seconds, the kernel restarts the iPhone. The name of the stuck service follows “checkins from”. Hence the classic pattern: a restart roughly every three minutes.
“thermalmonitord”: the service that monitors the temperature sensors. If it appears on its own, the hang may be software. If it comes with “Missing sensor(s):” followed by one or more codes, the iPhone is no longer receiving data from a sensor. On older models, repair technicians have learned to match these codes to a part: Mic1 or Prs0 to the charging port flex, Mic2 to the side button flex, TG0B to the battery. These mappings change from one model to the next, and no reliable table has been published for the iPhone 18 Pro. Keep the principle in mind: a missing sensor almost always points to a physical problem (flex cable, part, moisture) that no update will fix.
“SEP” or “Secure Enclave”: the security chip that handles Face ID, among other things. An iPhone 18 Pro Max owner reported a “SEP Panic” entry after a Face ID failure on the MacRumors forums. That is consistent with the bug fixed in iOS 27.0.1, though Apple has not confirmed it.
ANS2, NAND, power errors: storage or logic board, so a repair job.
Software bug or hardware fault: how can you tell?
Short answer: a crash tied to a specific action that goes away after an update or a restore is software; a message naming a missing sensor that survives a clean restore is hardware.
| What you see | Likely cause | What to do |
|---|---|---|
| Restart right after a Face ID failure in an app | iOS 27 bug acknowledged by Apple | Update to iOS 27.0.1 or later |
| Touch freeze after opening both Centers at once | iOS 27 bug, no spontaneous restart | Force restart, then update |
| Restarts about every 3 minutes, “Missing sensor(s)” | Sensor, flex cable or battery | Replacement or repair, logs in hand |
| “userspace watchdog timeout” naming a different service each time | Unstable system, often software | Free up space, then restore |
| Restarts that began after restoring a backup | App, profile or setting carried over | Remove profiles and suspicious apps, then set up as new |
| Apple logo / black screen loop without reaching the Lock Screen | Corrupted system or hardware failure | Recovery mode, then DFU, then repair |
| SEP, NAND or ANS2 entries repeated after a restore | Security chip, storage or logic board | Go straight to repair |
Before you start
Back up while the iPhone stays on: Settings > [your name] > iCloud > iCloud Backup > Back Up Now, or over a cable (Finder on a Mac, the Apple Devices app on a PC). Also export two or three panic-full files: a restore erases them, and they are your best evidence at the repair desk.
Fix 1: install the latest version of iOS
This is the only official fix: Settings > General > Software Update. If the iPhone restarts during the download, update over a cable from Finder or the Apple Devices app.
In the meantime, when Face ID fails inside an app, enter your passcode instead of trying again. Apple Support has also advised some users to reset Face ID (Settings > Face ID & Passcode > Reset Face ID): it may make crashes less frequent, but it does not fix the bug.
How to check: no new panic-full file after several deliberate Face ID failures in the Passwords app.
Fix 2: free up storage space
An iPhone that is nearly full struggles to write its system files, which can stall services until the watchdog kicks in. In Settings > General > iPhone Storage, aim for at least 10% free space; the recommendations shown at the top usually do most of the work.
Fix 3: remove profiles, VPNs and suspicious apps
Configuration profiles, VPNs and filtering apps hook deep into the system. In Settings > General > VPN & Device Management, delete any profile you don’t recognize. Also uninstall the apps you added just before the first restarts, especially VPNs, blockers and “cleaner” tools. A profile installed by your employer may be running your work email: ask before removing it.
Fix 4: reset all settings
Settings > General > Transfer or Reset iPhone > Reset > Reset All Settings. Network, Wi-Fi, privacy and Face ID settings start from scratch, without touching your photos or apps. Useful when a setting carried over from an old iPhone seems to be the culprit.
Fix 5: restore iOS over a cable (recovery mode, then DFU)
For an iPhone stuck in a loop or crashes that won’t go away, reinstall iOS from a computer.
Recovery mode
- Connect the iPhone to an up-to-date Mac (Finder) or to a PC with the Apple Devices app (iTunes on older versions of Windows).
- Quickly press volume up, then quickly press volume down, then press and hold the side button. Don’t let go when the Apple logo appears: wait for the screen asking you to connect to a computer.
- Choose Update first, which reinstalls iOS without erasing your data. If that is not enough, start again and choose Restore, which erases everything.
If the download takes more than 15 minutes, the iPhone exits this mode on its own. Let the download finish, then repeat step 2.
DFU mode
DFU mode also rewrites the boot firmware. Apple does not document it for the general public, but technicians use it. The sequence below is the one repair shops apply to Face ID iPhones; the timings are approximate and may take a few attempts. With the iPhone connected: volume up, volume down, then hold the side button until the screen goes black. Keep holding the side button and also hold volume down for a few seconds. Release the side button while still holding volume down until the computer reports a device to restore, with the iPhone screen staying black. If the Apple logo appears, start over.
Risk: everything gets erased, so a backup is essential.
Fix 6: set up as a new iPhone
After a restore, don’t bring the backup back right away. Set up the iPhone as new, sign in only to your Apple Account (photos, contacts and messages come back through iCloud) and use it for two or three days. No crashes: the cause was in the backup, so reinstall your apps one by one. Crashes continue on a clean, up-to-date iPhone: the problem is hardware.
When should you ask for an iPhone 18 Pro replacement, and what should you bring?
Short answer: as soon as restarts persist on the latest version of iOS, or the logs name a missing sensor.
- iPhone bought from Apple less than 14 days ago: you can return it for a refund or have it exchanged in store. Get the restarts on record before that window closes.
- After that, the defect falls under Apple’s one-year limited warranty. Book an appointment in the Apple Support app.
- On top of that, consumer law in your country may give you rights against the seller. In the UK, the Consumer Rights Act lets you ask the retailer for a repair, replacement or refund when goods are faulty. In the EU, sellers owe a legal guarantee of conformity. If you bought the iPhone from a carrier or a retailer, that seller is the one to contact.
- AppleCare+ extends coverage and also covers accidental damage.
For the appointment, bring:
- two or three exported panic-full files, with the panicString line identified;
- a video of a restart, if you managed to film one;
- your iOS version and the list of fixes you have already tried.
The technician can run Apple diagnostics remotely or in store. Mention that the iPhone has been restored and set up as new: that way you won’t be sent home with nothing more than advice to update. On the other hand, if your crashes match the Face ID bug exactly, a replacement is pointless: 9to5Mac judged that the replacements offered before the fix shipped were probably misguided.
In Africa, Apple works mainly through Apple Authorized Service Providers, listed on its support site. Its warranty terms allow it to limit service to the country or region of purchase: an iPhone bought in Europe might only be covered in the European Economic Area. Whether you are in Lagos, Nairobi or Accra, call the authorized provider before going, with the serial number at hand.
Full specs for each model are in our iPhone 18 Pro and iPhone 18 Pro Max spec sheets.
Keeping it from happening again
Let iOS install bug-fix releases automatically as soon as they come out: the option is in Settings > General > Software Update. Keep a comfortable storage margin and never install a profile picked up from a website you don’t know. An occasional panic-full file is nothing to worry about; it is repeated files that should set off alarms.
If your iPhone freezes in certain apps without restarting, our guide to Messages showing a black screen and a frozen Settings app covers another common scenario.
FAQ
Is my iPhone 18 Pro defective if it restarts on its own?
Not necessarily. Most cases come down to an iOS 27 bug tied to Face ID, fixed in iOS 27.0.1. Restarts that persist on the latest version, with a missing sensor in the logs, point more toward a hardware fault.
Does iOS 27.0.1 fix every restart?
No. It only targets restarts triggered by a failed Face ID authentication on the two Pro models.
What does “panic-full” mean in Analytics Data?
It is the report iOS writes when its kernel crashes and forces a restart, one file per crash.
What does “Missing sensor(s)” mean in a panic-full log?
The iPhone is no longer receiving data from a sensor. It is almost always hardware: flex cable, connector, battery or liquid.
What does “userspace watchdog timeout” mean?
A system service stayed silent for about 180 seconds and the kernel restarted the iPhone as a safety measure.
Is the iPhone 18 Pro Max affected?
Yes, the iOS 27.0.1 release notes name it. Nothing suggests that other iPhone 18 models are affected by this Face ID bug.
Does a restore erase panic-full files?
Yes. Export them first: you will need them for the repair.
Can I get my iPhone 18 Pro replaced for this problem?
Yes: within 14 days of buying from Apple, then under Apple’s warranty or your local consumer rights, with the logs to back you up.
Your iPhone 18 Pro keeps restarting even after the update? Tell us in the comments what your panic-full file says: reader reports help narrow down hardware failures. And for the other defects reported on this model, see our roundup of every known iPhone 18 Pro problem and how to fix it.
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