I have a project connecting to a display via uart and to a 328p, and have been experiencing the same issue. Originally, I was using the third (uart /serial 2) for display and it functioned well. I managed to get comms with uno on the second (serial 1) port to work, but after and update... It receive...

I get the same error trying to switch between 2 thingspeak channel updates. Honestly, it's my experience that on this chipset ....this just happens 60% of the time. I just don't get it. I'd get out of arduino IDE but it's a senior design project and I port my code again in time.

Someone will eventually grind it out and make a c/c++ friendly build devoid of RTOS and everyone will use that. ESPRESSIF will scratch their heads as to why people want to be able to control and use their own hardware...