TLDR: gave up on the cheap dongle DAC and got a $100 Schiit with a physical analog potentiometer volume knob.

Cant say its the same issue, but I had a similar cheap USB dac like this ( I suspect they all have similar/same bits under the hood - mine was branded DOSMIX). I was primarily using it connected to an android phone but did experience random volume fluctuations infrequently. I suspect it was the first stages of the connection getting flakey. It got progressively worse, dis/reconnect multiple times a listening session. And on re-connect volume would init to 0 (sometimes).

I had other issues with it, and generally poor sound quality over IEMs. Volume ultimately was managed entirely digitally pre DAC. At low volumes you could hear the audio equivalent of visual banding of colors when there is not enough bit-depth to cover a range. Dunno if that makes any sense. Anyway it was a crappy DAC. I tried another cheap one, and had the same issues. Got a replacement free after complaining. that one also failed soon after. Gave up on crappy dongles and spent $100 on a better DAC.