Yes. We discovered the problem in March 2020.
The new playlist mechanism (as of Mosaic 1.1.0) periodically refreshes track metadata so that what is shown in the list is always current. This is breaking with some UPnP servers as we aren’t being given ID information that remains constant through all rescan scenarios. So in other words, the track identifier that we’re given today will get reset with the next rescan and will likely end up being assigned to a different track. We may end up removing the refresh mechanism for UPnP tracks which would make it behave like the old Rossini app.
Playlists will never be perfect with UPnP as there’s no surefire way to fingerprint a track. Any change to track metadata and/or location on storage will likely cause the server software to see it as a completely new file and that will likely break any link that we’re able to establish. This is one of the fundamental limitations of UPnP and one of the reasons why I’m a big supporter of Roon for those who make heavy use of playlist features from their local library.