Are you facing the same issue? Many others surely are. Today, while checking my communities i observed some unknown communities which were in the list. Strange it was. Moreover, when visited, the community provided an option to ‘join the community’. That was definitely a bad bug.
When manually joined and then unjoined, the communities were removed from the my communities page. If you are facing similar issue, you should follow the same procedure to remove such communities from your my communities page.