Just if someone else made also that irritating experience:
From time to time a feather on a breadboard seems to stop operating.
Today was such “stop”. I tried to analyze the topic and found, that the reset pin (J3/1) sticks to around 0.7V, while on other boards it’s about 2.2/2.3V. Pressing SW1/RST pulls it down to 0V, so I concluded, it’s not caused by a damaged button.
having a closer look then exposed the real cause:
Some leftovers from the solder-flux.
I cleaned it, and the voltage is now also about 2.2V ;-).
OK, yes, always remove the solder-flux with a cleaner.
Especially, for device in “high resistance” technology to save energy.
But sometimes some are lazy …