ok first create a community with 2 members (e.g. user1 and user2, with user1 as the owner) user2 then changes their username to "user3" at the same time user1 transfers ownership to "user2" then both users can leave (i think because the owner is set to user2 but user2 doesn't exist anymore)
ok but if it isn't working it's probably because you didn't get the timing right. I always start by changing the username and then about 1 second later transfer the ownership (if you go too late or early it won't work)
user2 then changes their username to "user3" at the same time user1 transfers ownership to "user2"
then both users can leave
(i think because the owner is set to user2 but user2 doesn't exist anymore)