I’m having a similar problem. No sound output from USB DAC when using Squeezelite.
With other software (not SL) I do get playback from my DAC.
I see two soundcards in my Pi setup: soundcard 0 is default pi, bcm 2835
soundcard 1 is the DAC name
alsa is set to 100%
both outputs work and produce sound when not using Squeezelite, with other network software (playback software such as Roon Bridge, HQP NAA, etc.
When I try to playback with SL, I get no sound output. Acc’d to LMS setup, everything looks okay.
Any ideas?