Hi Mat,
if you flash my code above once with SYSTEM_THREAD(ENABLED) and have it run, the next OTA flash will turn on magenta, quickly flash the new code, go back from magenta to cyan breathing without reboot, still Serial.printing for several seconds and only after a while (10 to 15sec) reboot into the newly flashed firmware.
I’d see this unexpected, since a “normal” OTA without the previous code running under SYSTEM_THREAD(ENABLED) immediately reboots into the new firmware afte magenta goes off.
I tested this about half a dozend times with and without - each time about 20sec from magenta to reboot with and less than 5sec without SYSTEM_THREAD(ENABLED) on previous firmware.