This is kind of where I was going when I suggested sample rate change- perhaps I should have worded it as losing synch or not being locked. I wonder if you have something going on where the clocks are losing synch?
You mentioned a mix- is this a DAW setup? Are you running any memory intensive plugins or seeing large latencies in any other way? Just trying to learn from your experience here as I’ve not used a monitor with internal DAC before.