There is some logspam from loginwiki (about 10/min) saying "MediaWiki\Auth\AuthManager::autoCreateUser: {username} failed with message Username entered already in use. Please choose a different name.. This is probably caused by a race condition between CentralAuthCreateLocalAccountJob and SpecialCentralAutoLogin. The autocreate logic tries to handle such races nicely: it checks for existence and handles it as a non-error; then does a bunch of other checks and applies locks; then adds the user to the DB and on failure checks whether the user exists already and again handles that as a non-error; only if that all fails will it log an error. Apparently both of those checks manage to fail somehow.