Hello there,
I use MODx Revolution 2.0.7-pl (traditional) on a Modx qualified server.
I have a category system that looks like this:
Snippets
->Swydo
->Registreren
->Ajax Snippets
->Form Hooks
The categories Ajax Snippets and Form Hooks were containing the snippets I created.
Also the category Registreren had a snippet.
When i removed that snippet the category Registreren was removed from the sippet tree, while the sub categories still contained snippets. I first thought they disappeared, but they still were in the Modx database.
I now created a temporary snippet called "testsnippet" so that the category is displayed and i can acces all the snippets i need to acces.
Conclusion: You need a direct snippet in a category for the category to be shown, if the sub categories but the parent category doesn’t contain a snippet, the categories are hidden from the tree. This seems a bug to me.