When i tried to rename myself, i got an exception. Trying to insert the log entry required creating an actor for my old username, which resulted in an exception. I guess this doesn't usually happen as usually the user being renamed is not the same as the user doing the renaming.
[5993263718ff80a7c4a6d063] /w/index.php/Special:RenameUser CannotCreateActorException: Failed to create actor ID for user_id=1 user_name="Bawolff"
Backtrace:
from /var/www/html/w/includes/user/ActorStore.php(434)
#0 /var/www/html/w/includes/logging/ManualLogEntry.php(319): MediaWiki\User\ActorStore->acquireActorId()
#1 /var/www/html/w/includes/RenameUser/RenameuserSQL.php(335): ManualLogEntry->insert()
#2 /var/www/html/w/includes/specials/SpecialRenameuser.php(252): MediaWiki\RenameUser\RenameuserSQL->rename()
#3 /var/www/html/w/includes/specialpage/SpecialPage.php(701): SpecialRenameuser->execute()
#4 /var/www/html/w/includes/specialpage/SpecialPageFactory.php(1564): SpecialPage->run()
#5 /var/www/html/w/includes/MediaWiki.php(344): MediaWiki\SpecialPage\SpecialPageFactory->executePath()
#6 /var/www/html/w/includes/MediaWiki.php(948): MediaWiki->performRequest()
#7 /var/www/html/w/includes/MediaWiki.php(597): MediaWiki->main()
#8 /var/www/html/w/index.php(50): MediaWiki->run()
#9 /var/www/html/w/index.php(46): wfIndexMain()
#10 {main}This happens both on master with core rename functionality and on 1.39 with renameuser extension.