Normal behavior: All URL rewrites of categories work.
What I am getting: Categories that have subcategories do not work. But categories that have no subcategory work fine.
What I tried:
Used Oleg Kowal URL rewrites to regenerate them all. (deleted all URL rewrites before that).
Disabled all custom extensions.
What I suspect: I think Magepow categories extension messed it somehow in the database. But, no way to tell if it is the case.
Any help is much appreciated