For a bit of context here, I'm the owner of the community. On first join, this user had two messages in our #joins channel which has happened to me before, but never ended in this result. We tried to help by kicking and banning and then unbanning but the communities would keep coming back and adding one more on their side.
When kicked or banned, they also seem like they haven't left the community even though they have. They're still in our list of members, but we can't kick them, ban them or add roles or anything because they aren't in the server.
This is the weirdest glitch I've ever seen.
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Comment by @IAmTheNerdNextDoor