I have seen such messages if a manager (gvmd) database was at a database scheme version from versions < 20.08, a migration was done to >= 20.08 but the “old” report formats at $prefix/var/lib/gvm/gvmd/ was missing for the migration to the new location $prefix/var/lib/gvm/data-objects/gvmd/.
The following existing topic has some more background info: