There was a failure in rpl_delayed_slave after recent MDEV-14528 commit.
The parallel applier should not set its
Relay_log::last_master_timestamp from Format-descriptor log event.
The latter may reflect a deep past so Seconds-behind-master will be
computed through it and displayed all time while the first possibly
"slow" group of events is executed.

The main MDEV-14528 is refined, rpl_delayed_slave now passes also
in the parallel mode.