It’s impossible to say without more data. A good case would be there are irrelevant leftover dindex files, referencing irrelevant dblock files. If lost dblock files are actually in use, then backup damage is present.
Recovering by purging files explains how to use list-broken-files. GUI Commandline is the simplest way.
If you prefer, you can post a link to a database bug report to get a manual inspection (or try one yourself).