I had a category group with a sub category that was archived. Once I deleted the category group, the archived sub category showed up again on the budget page. Now I removed the category group from the archived category and now it's fixed.

Edit: No, it wasn't fixed with that. I had to unarchive the cat and then archive it again.

Edit 2: No, still here. I guess I have to live with this cat I don't need anymore :(