The server monitor is written to log at INFO level only when relevant server state has changed. Mostly it does a good job, but there are spurious log messages in one particular case, when a replica set member has multiple tags. The server does not ensure that those tags are provided in the isMaster response in the same order every time, and every time it changes the driver sees it as a relevant server state change, and so logs it. This results in spurious messages like:

... INFO ...Monitor thread successfully connected to server with description ServerDescription...

This could be fixed in the driver by ensuring a stable ordering of the tag sets (e.g. by sorting the tags by tag name)