Looking around some more, I think you might have tried to create a new category in the wrong way. I think you can just start a new entry and leave it blank, but for the following code:
[[Category:Category Name]]
And for a new subcategory:
[[Category:Category Name::Subcategory Name]]
Or create that category’s first entry at the same time, of course.
To change an existing entry, I think you just change that coding at the top to reflect a/the new category or subcategory.
I see where the “Mt. Eckstein” entry has a category code of “Geographic Places” at the top, yet it’s listed in that subcategory. You might have to restart by deleting all that category stuff and recreating them.
I hate the whole Wiki syntax. It’s ridiculously daunting for the average user who first looks at it, and thus really limits Wiki participation. It simply need not be that way.