Though this thread is old, I thought I’d add something here.
I have the new Seeed MIDI Synth, which includes the Xiao ESP32C3 and a SAM2695 synth module. The thing has a built in speaker as well as a 3.5 mm stereo headphone port. It gets its power from USB, the very port of the ESP32C3. So I program it through the same port that provides power for the ESP32C3, which further powers the rest of the synth. That’s probably too much. Either that or the synth produces noise in the data stream. Uploading programs from Arduino IDE fails almost all the time. The ESP32C3 goes nicely into bootloader mode with the buttons. But uploading ends in errors like described in this thread.
The solution seems to be to disconnect the ESP32C3 from everything else, upload the program, then reconnect everything again. It might also be worth to use a short, high quality USB cable.