@jiggow if you look next to categories Search Box there's a Settings icon that little wheel looking thing.
Click on that icon and update the categories from there, it should give you the option to do so (it gave it to me).
Also try deleting the categories directory on the garage sale folder usually located on a similar path:
hard drive name/users/user_name/library/containers(it's a hidden folder)/com.iwascoding.garagesale7/data/library/application support/garage sale/
I was having the same problem and this resolve it.
It's a clear bug, it happens a lot but i always just manage to find this gotchas (tech background).
This was a major find, I was losing my brains because collections kept disappearing from random listings after closing/opening GS7 and for no apparent reason.