USB Audio Oddity

Solution 1:

I had a similar issue on High Sierra with a Line6 interface; slightly different as the audio would fail if I left the machine alone for a while. It didn't sleep, my machines never do, but after some unknown period of time the audio would fail.
When it did this it would also cause any video to fail too - endlessly spinning pizza wheel when on VLC or YouTube etc.

My temporary fix at the time was to toggle my output's output frequency in Audio MIDI Setup, 44.1 to 48 & back again [or vice versa] which would be fine for another day or so.

The issue went away with Mojave [as did many other issues High Sierra was plagued with].