This is a difficult one to investigate because I can't duplicate the error.
Two of our members have had this happen. They've both been very familiar with the gallery.
They try to go to a category, but can't see any of the subcategories within in. They both have permissions to see it and nothing has been changed.
This is a screenshot of it.
Both users were able to log and come back later to find it working again.
Any ideas what's causing this?