I had a weird state of a table where dropping it would return the error ‘performing cache lookup failed for relation '

what fixed it was looking up the oid and then just removing all its entries.

select from pg_depend where objid = MY_OID;

delete from pg_class where oid = MY_OID;
delete from pg_depend where objid = MY_OID;
delete from pg_constraint where conrelid = MY_OID;

might be very invasive, the state of that dataset was not too important.