"I'm Back"! The problem still rears its ugly head, I've tried 3 different Micro-USB cables (or 4). I have a whole pile of logs and a few screenshots. I've got a 3A+ to an MPmini .v1. I have v.29.50b firmware on the MPmini. Last night I had 2 entries in /dev /ttyAMA0 & /ttyACM0. /ttyACM0 was there last evening, gone this morning, restarted OP, it's back! WTH? It sounds like I might try the new RC, but I've never done one before...How to?
I also have another Pi3A+ CREnder3Pro, from the same image, same updates, running a different version of Debian. ???
I did the "dmesg" command, after a reboot. I've pulled all the "USB" message lines out of that 4 pages of entries. It is like reading a "Wireshark" scan, in 60 seconds. Wheee. I've attached those for your parusel. I'm still seeing 2 entries in /dev/ttyACM0 and /dev/ttyAMA0 ... yuk.
I did those other changes in the Serial Connection section, as you suggested @foosel
I know my way around OP that I'm quick to find and quick to try.