MDEV-19964 patch did not check flags2_inited before
to access flags2 itself.
The latter may be randomly non-zero (see Query_log_event constructor) which
eventulizes on rpl.rpl_mariadb_slave_capability with the following mismatch pattern:
where the '+' extra is cause by the random flags2.
The case should be fixed with following the pattern of first checking flags2_inited.