If i remember correctly there are some quests which have quest steps that have a feature that makes every monster around you aggro on you immediately, as if you were constantly spamming Swash Buckling regardless where you go.
By never completing these quest steps this perma-aggro feature never gets canceled, thus people have perma-aggro on everything around them, even if they go on another map or log out.
It’s not really a bug, i’d call it a quest exploit.