After dbstore2002 has been added more than one instance (x1 and s2) - complete it with as many instances as possible using GTID (probably 7 will not fit, but we could have 4 or 5), and start using GTID on them.
This will validate the multi-instance beyond just 2 hosts.
Also delete the multi-source main instance it still holds.
- s1
- s2
- s3
- s4
- x1
- ...