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akil_vohra
User level: Level 1 (4 points)

Apple Watch keeps restarting: kernel panic "AppleHIDTransportProtocolSCMMailbox invalid checksum"

My Apple Watch has restarted on its own ever since I bought it, roughly every 4-5 hours. It's intermittent, with no obvious trigger. I pulled the crash logs, and all of them show the same kernel panic. Is anyone else seeing this exact error?


Device: Apple Watch (model identifier Watch7,18; Series 11), paired with an iPhone on iOS 27


The panic, identical in every log:

[AppleHIDTransportProtocolSCMMailbox::parseNewReadBytes] Invalid message read from the FIFO ID 1, interface ID 4, report ID 0x52, transfer ID 0xF2: invalid checksum (read: 0xD28F9CF1, calculated: 0xD2901CF1)


What I've seen so far:

- 3 panics in about 13 hours

- 2 on watchOS 26.6, while the watch was erased and sitting on the Setup screen, with no apps or data on it

- 1 on watchOS 27.0.1 after updating, in normal paired use

- Each one about 20-26 seconds after the watch woke from sleep

- The last driver loaded before every panic was AppleMultitouchDriver (the touchscreen driver)

- Memory pressure was false in all of them, and a watchdog reset follows each panic


What I've already tried:

- Unpaired and erased the watch, then set it up again

- Updated to watchOS 27.0.1 (the version that fixed the Series 12 / Ultra 4 reboot bug; this is a different panic)

- Two visits to an authorised service centre; the case is now escalated with Apple Support

- Filed in Feedback Assistant as ***


Questions:

  1. Has anyone else seen "AppleHIDTransportProtocolSCMMailbox" or "invalid checksum" in their watch panic logs?
  2. If so, which model and watchOS version, and did Apple repair or replace the watch?


How to check your own logs: on the iPhone, go to Settings > Privacy & Security > Analytics & Improvements > Analytics Data and look for files starting with "panic-full". Open one and search for "HIDTransport".



[Edited by Moderator]

Posted on Oct 19, 2026 9:47 PM

2 replies

akil_vohra Author
User level: Level 1 (4 points)

Oct 20, 2026 7:57 AM in response to Branta_uk

Thanks — yes, it's still under warranty.


Honestly, it's been frustrating. The local authorised service centre wasn't able to help much: their tests don't reproduce the restarts, so no one there was willing to raise a case on my behalf, even with the crash logs in hand. After several attempts I managed to get on a call with Apple Support directly, and the case is now escalated with them.


I'm not asking anyone here to diagnose it. I posted the exact panic string so that anyone else with the same random restarts can search for it and confirm, and so this thread can serve as a reference for someone who hits the exact issue in future.


I've had the logs read through with the help of LLMs; this is an interpretation, not Apple's diagnosis.


What the panic logs tell us:

  1. It's a kernel panic, not an app crash. The watch's main processor talks to an internal input co-processor over a small message channel (a "mailbox"). Every message carries a checksum. The driver that reads these messages (AppleHIDTransportProtocolSCMMailbox) received one whose checksum didn't match its contents (read 0xD28F9CF1, calculated 0xD2901CF1), treated it as corrupted, and deliberately panicked the kernel.
  2. The panic triggers a watchdog reset about 30 seconds later, and that's the restart I see.
  3. It's the identical failure in every log, on two watchOS versions (26.6 and 27.0.1), on an erased watch sitting on the Setup screen, and in normal paired use. That rules out apps, settings, data and the iPhone/watch version mismatch.
  4. In every case the last driver loaded was the touchscreen driver (AppleMultitouchDriver), about 20–26 seconds after the watch woke from sleep. That points at the touch or input path between the co-processor and the main chip, but only Apple can confirm whether it's hardware or firmware.
Branta_uk
User level: Level 7 (33,350 points)

Oct 20, 2026 7:41 AM in response to akil_vohra

If this has been happening since you bought the watch I hope it is still in warranty.


The crash logs can only be interpreted by the developers and maybe the very top level support. For anyone else they are meaningless.

What I've already tried:
- Unpaired and erased the watch, then set it up again
- Updated to watchOS 27.0.1 (the version that fixed the Series 12 / Ultra 4 reboot bug; this is a different panic)
- Two visits to an authorised service centre; the case is now escalated with Apple Support
- Filed in Feedback Assistant as ***

You have followed all the appropriate steps and it has been escalated to Apple Support. There is nothing useful anyone can add here.

Originally posted at discussions.apple.com/thread/256379347