Crowd User removed from Confluence group upon logging into Confluence
Right after synchronizing a Crowd User Directory a user appears as a member of a group. When the user logs in they are removed from the group.
A group exists in Crowd with the same name but different casing.
Create a new Crowd User Directory with the same settings. Sync this Directory and disable the old one.
There is a request open to eliminate this behavior. You may vote for it if you like so it will get more attention from the development team.