A 21.0 system was installed and started up. Then a copy of a 12.x database was copied to the same database. Once this was done, search results were very strange:
Release : 21.0.1
By migrating/changing the JCPs and pointing them to what was then basically a different database, the lucene index that is used for searching was corrupted, having some information from the original database and some from the new database. This cased the names and id numbers being different in the indexcache for the JCP.
The resolution for this was the following:
This allowed the lucene index to rebuild itself and then the search worked correctly.