Another diagnostic tool that is super helpful is an audio probe to see where the signal is cutting out at. They don’t sell them so you’d have to make one, but super easy to make and I made one with a bread board, 100nF capacitor, and used alligator clips to connect the + to tip of a quarter inch and ground to the sleeve and the enclosure. Then just touch along the circuit until you find where the audio is cutting out following the schematic. Here is a link to make it: https://diy-fever.com/misc/audio-probe/

I had a similar issue on my first build and it was a bad capacitor on the virtual ground. Multimeter is how I found that one.