I’ve had this issue for a few months, some details in Roon grouping and synchronisation of playback.
Since posting that I’ve been doing further digging and it’s always the Muso 2 that gets behind (Muso Qb and ND5XS2 are the other devices). A quick way to reset it is to change the Zone grouping delay, eg add 1ms, but that doesn’t last long though.
Whilst sorry to hear that you’re having this problem, it’s very annoying, it’s good that someone else apart from me has it; it is real! I have a ticket on the Roon forum that is getting some attention and when I next post there I will mention that there is at least one other person who has this.