In our Jira Software Server 8.13.1 we have one single user which can not removed from the list of watchers of any issue. Whenever the user is removed or removes himself from the watchers of an issue he is immediatly added again to the list of watchers for that issue by an unkown mechanism.
Even after we set that user to inactive and removed all project roles, it was still not possible to remove the user from the list oft watchers. No logs shows anything unusual.
Has anybody ever monitored a similar behaviour?