DBA_OBJECTS slow in PDB only

DB is 19.25 on Linux 8

What we see is that a simple count of objects of DBA_OBJECTS in Root's container takes max. 1 second, but it takes 5 minutes in a PDB

Granted there are more objects in the PDB but the timing difference is of a total different order

select count(*) from dba_objects ;

What can explain such differences ? We see this extreme behaviour in one database only, other databases are not that slow, but just slow as well.