Maybe somebody is interested, so I report back what I have found so far:
I did 'git bisect' on esp32-arduino pointing at the following commit: 22b427df IDF release/v3.3 (#3672) So the change came from ESP IDF, not esp32-arduino (which is no surprise).
I assume the error came from my (wrong) attempt to change the channel esp-now is working to channel #4. Possibly the older IDF version just ignored the issue, so esp-now *did* send parameters to my orchestra of a couple of ESP32 musical instruments configuring and synchronizing them, but just used channel 1 instead of channel 4. As the music started well I assumed everything was ok. I could not really test this theory, but I have my reasons to think so. Probably the newer IDF version just checks parameters better and refuses to send. Error messages instead of music
As a workaround I set the channel to 0 or 1 and it works like it did before.
A lot of googling showed me, that it *is* difficult to change the radio channel for esp-now and I'm not really sure yet, if it *is* possible at all. I would be happy for any informations on the matter.
btw: I do *not* use wifi for anything else but esp-now in these instruments. No AP.
questions:
Did somebody succesfully change esp-now radio channel to anything other then 1 or 0?
Did anybody try esp-now related tests with SDR?