Following the documentation here:

https://mariadb.com/kb/en/multi-source-replication/

The replicate- variables do not work if the connection_name has an underscore. Considering the example on the page:

mysqld --main_connection.replicate_do_db=main_database

If that were to be put in a config file, it would not be loaded because of the underscore in 'main_connection'. I have tried quoting numerous ways and was advised to make a bug report, "There is something about replacing _ with - (or vice versa) in option names, probably that is interfering"