There isn't an "s3/s6" replication lag. There's an s3 replication lag and an s6 replication lag. If your query was running on an s3 database, and you checked the replication lag there, you might have missed the fact that s6, on the same server, was lagged.
To be 100% precise, I check replag on the language the script works for. In this particular case it was russian. In order to check the replag my script compares current time to the last edit time in the language database.
Am I right that I need to check s3 replag as well for this particular case but do not have to check replag on s2, s5 and s1?
mashiah