I’ve had some dom0 memory trouble once. It impaired video playback.
No matter how many memory I assigned to dom0 (I’ve tryed 16GB) every few seconds it spiked.
I’ve seen it with conky memory graph, othervise I was in no knowledge of that.
There is simple conky config at github for dom0 - can you try it and se if you have dom0 memory spikes?
PS: it would be nice to se sys-usb memory graph to, but I don’t know how to do it now and can’t test it as Im away from home