More details.
The phone restarts because of the watchdog, which kicks in a reboots the phone in response to thermalmonitord freezing up.
"panicString" : "panic(cpu 0 caller 0xfffffff01de8f60c): userspace watchdog timeout: no successful checkins from thermalmonitord (2 induced crashes) \nservice returned not alive with context : is_alive_func returned unhealthy
The freezing up of thermalmonitord is triggered by the microphone reported as being faulty:
"termination" : {"flags":0,"indicator":"monitoring timed out for service","code":1,"namespace":"WATCHDOG","details":["(1 monitored services unresponsive): checkin with service: thermalmonitord (0 induced crashes) returned not alive with context:","is_alive_func returned unhealthy : current 6fffffffffff, mask 1fffffffffff, expected 1fffffffffff. SD: 1 BC: 1 RC: 0 BS: 1, Missing sensor(s): mic1","no successful checkins since 84 seconds ago, has not exited since first loaded"]},
thermalmonitord in turn should never freeze in response to a hardware error, this is an iOS software bug.
In turn, the enabling of the microphone and the subsequent freeze of thermalmonitord only starts happening after you unlock the phone for the first time after reboot. In the early days of iPhone subsystems would be left unpowered to save battery power when not in use, it appears Apple no longer does this and instead powers up unnecessary subsystems the moment you unlock the phone, which explains why battery life gets worse and worse over time.
The Apple authorised reseller has confirmed this is a common hardware fault with the iPhone SE, where prior attempts to replace the battery can result in subsequent further hardware damage. Will report back whether they're able to fix it without logging into the phone.
The impact of the thermalmonitord freeze is avoidable data loss - instead of leaving faulty subsystems switched off allowing the rest of the phone to keep working, faulty hardware triggers a cascading failure of faulty software, and the backup is no longer possible.
