Followed repositories still show up in the dashboard as following after removing access to them
Followed private repositories still show up in the dashboard/repositories block after removing your access to them.
Since you do not have access to them anymore, your unable to unfollow the repositories.
Proper behavior when removing access to a private repository should be to unfollow the repository.
In my case I am still following 5+ private repositories that I removed my access to - which I am unable to access and unfollow now.