I've just added a comment but accidentally set the visibility to a group of which I am not a member. Therefore I cannot see this comment! As admin, I also cannot see the comment.

I can, as admin, add myself temporarily to that group to delete the comment, but it seems that admin perhaps should be able to see all comments regardless of their visibility. This might also be useful for managers of large teams.

Therefore I propose a new permission 'View all comments' which overrides the usual visibility of comments.