IMO, you’ve had what Roon calls ‘latent corruption’ for a while and the upgrade to a new Roon version uncovered that. Any Backup you have done while this corruption existed has, of course, been corrupted. You can’t find an un-corrupted Backup because the condition has existed long enough so that all the good Backups have been overlaid,
If that’s true in your case, it’s something that has always been a problem.