FWIW I have exactly the same issue. I had thought that it was fixed, as it went more than 24hrs without doing it. But I was woken early this morning by the Nokia startup sound!
Reading elsewhere online there seems to be a few people with the same issue. Hopefully this is something that can be fixed OTA, and not something that required warranty replacement.
Tried booting into safe mode, but aslo that did not solve the problem.
Any ideas? Any way to log what causes a reboot?
Reboots do not occur while phone is charging via PC with adb logcat connection open (hoped to see what causes the reboot...)
Did see the following lines however:
07-20 13:57:27.544 1177 1254 I BatteryService: shutdownIfLowCurrentLocked mBatteryMinVoltage = -1 , isNegativeCurrent = true , batteryVoltage = 4227 , isSystemReady = true
07-20 13:57:27.562 5039 5039 I [BatteryProtectApp]: DetectBatteryService: mMaxTempShutDown : false
07-20 13:57:27.562 5039 5039 I [BatteryProtectApp]: DetectBatteryService: mLowTempShutDown : false
Could one of these be the cause?
My phone restarts after a few minutes of being plugged into any fast charger - either the one that was supplied by Nokia or another make.
The phone does not restart when connected to an old style charger without fast charge.
I had to sent my phone for repair, after receiving it back after 3 weeks, the problem is solved (incl. another problem: SIM2 was not working).