yes the related GUI that should use it do not get the proper code meanwhile with ESP do not have any issue.
So if the start-stop-message is not transmitted well, the GUI doesn't react.
Baudrate, i can try but for my system I need 115200.
And here where he has similar, i see baud is different.
https://forum.arduino.cc/t/serial-flush-doesnt-wait-for-the-end-of-the-transmission/144094
To me is really an CH340 issue, maybe the oscillator.