My company recently ran tests on two Pi 4Bs in a temp chamber with camera attached.
Ran 1000 hours at 70C ambient - CPU around 80-82C No issues. (power always on)
Ran 1000 hours hot/cold cycle -25C to +60C - 8 hour cycle, 4 cold, 4 hot. No issues. (power always on)
Then we tried cold start at -25C, -15C, -10C temps.
Temp chamber soak at these temps for 1 hour, Pi powered off then switched on.
Seeing Ethernet failure and slow boot times at -15C and below. Likely due to Ethernet/USB controller chip ( 0C - 70C rated) When Pi is powered on, say at 0C and then cooled down (with power) works OK at these temps - maybe self-heating from chip keeps it going?
We don't think that condensation on RJ45 Ethernet or SD card contacts may cause this - need to investigate.
Power adapter is also inside chamber - maybe that is weak link?
Anybody else have experience with cold start up of a Pi board?