After migration from 10.4.18 to 10.4.25 the replication lag.
When I look at metadata_lock_info I see 2 "MDL_BACKUP_COMMIT" and 2 "MDL_BACKUP_TRANS_DML".
Those locks seems to be from the slave processes ...
If I kill the threads the slaves ptocesses are stopped.
If i restart the slaves, they are working some time (high IO rate) and the lMDL_BACKUP locks comes back and the replication lag again.
It is very urgent as it is on a production system.
The migration to 10.4.25 was OK on integration and pre-production systems and even on some other smaller production systems.
That system is working at 30000/50000 updates per minute.