I have an ESP-12f in my own PCB board powered by a power source. The module read some sensors, send the values through MQTT and go into deepSleep for 5 seconds. It works fine for some time (Sometimes 1 day, sometimes 1 hour) and then it block and send this data:
ets Jan 8 2013,rst cause:0, boot mode:(3,6)
unknown reset
ets_main.c
The same happen whit my other module.
Thanks,
Marcos