I have a Zero with the watchdog timer set. After about a day, the Zero locks up and the watchdog resets the board. However, no code is actually executed and the board just continues in a reset loop. Pressing the reset button has no effect. I have to unplug the USB to have the board boot back up normally again.
On some other boards, it appears to take a few days before the lockup but the effect is the same. Any idea what could be happening?