I’m not Roon, but I suspect the Roon database is corrupt and this may have happened sometime time.
B880 and onwards now checks for DB corruption (rather than having random failures) it also check for DB corruption before DB backup are made (which is important going forwards).
Do you recall when and what version of Roon was running when you made your latest backup?
I suspect it was pre B880, which was before these check were implemented.
All I can suggest is to attempt to restore from an old backup (before the DB was corrupted), if you don’t have one the only alternate is to start with a clean DB.
PS It importing to now be running Roon B884, if you’re unsure I would recommend going to the RoonLabs site, downloading it and performing a manual installation over the top of you existing install.