Don’t know if this is a factor for you, but I had a similar situation with two RPi/DietPi running Roon Bridge. I got lazy and instead of setting up both endpoints individually, I set up one and copied the result to the second and only changed the machine name and the static IP. That resulted in problems similar to the ones you describe.
In any event, the problems you are having sound to me like a Roon Bridge problem. Maybe deleting and reinstalling the bridge on both endpoints will resolve them.
For what it’s worth.