I have recently configured Active directory delegation and in one specific OU inherited permissions disappears from all users except one I have recently created for tests. Non of the users are a member of protected groups like: Enterprise Admins, Schema Admins, Domain Admins, Backup Operators etc.
It doesn't matter if the permissions are inherited or even if I directly applied them to the object. I've e tried to move users outside the OU and move it back but the problem remains.