This one is pretty in-depth: Grouped Playback exhibiting Clock Drift
but the issue was eventually resolved by the (very knowledgable) user.
also related to other hardware and eventually resolved.
And this one (but was also raised by Yannis): Grouped zones lose synchronisation over time
So there are not that many other reports but, in the last thread Mike mentions the fact that Roon is aware that syncing could be improved.
Before I’ll raise my own ticket / issue I’ll wait for BlueSound to update their RAAT implementation. According to Roon the latest update contains some improvements regarding the clocking / syncing of the slave device. So my hopes are on that update…