Could this have something to do with the USB chip that's recently been swapped:
"Note: Core2 currently has two CP2104/CH9102F A USB chip version, users can install the drivers (CH9102 and CP210x) that are compatible with two ICs at the same time to ensure that the device drivers work normally."
@jdonth Had the exact same problem.........after 3 hours of googling, finally found the issue. Take a look at this diff file:
https://git.koehlerweb.org/frodovdr/Sonoff-Tasmota/commit/8a764f86ee9f1129507f4654d07c7a7cb24cc87e
It's totally unrelated to this project. Just a bug that freaks out the IDE. Anyhow......a couple of lines need to be changed in :
\libraries\ESP8266Audio\src\libtinysoundfont\tsf.h
Hopefully it makes sense......Hope it helps....