With the introduction of build 880 Roon introduced a mechanism to check the integrity of your database:
Database corruption means that the records Roon is reading out of your database are different from what was originally written. This is uncommon and can happen for a variety of reasons, including failing hard drives. In some cases, corrupt records can remain in the user’s database undetected for some time, only being detected when an update ships that requires Roon to scan every record in the database.
These updates occur infrequently, which increases the risk of data loss – if the user has opted to only keep a few weeks of backups, the chances they have a usable backup drop significantly if the “latent” corruption isn’t detected for many months.
Unfortunately it seems as though your current problem is a consequence of the issue outlined in the second paragraph above, i.e. the backups you have tried to restore from contain “latent” corruption causing the restore to fail. All I can suggest (as a fellow Roon user) is that you try to restore from an older backup if you have one - one that was created before the latent corruption was introduced.
If you have already tried this then there’s not much you’ll be able to do other than to start over with a fresh database, but I’ll flag @support so they can confirm.