Is there a limit on the number of Child Categories a top level category can have? We have a top level category with 6 child categories. When I try to add a new category, this top level category is not in the Parent drop down list. Is this due to a limit or could there be something else going on?
I’m fairly sure there is no limit on the number of child categories a parent category can have. A parent category can definitely have more than 6 subcategories.
What version of Discourse are you on? Do you see any errors in your browser’s console when you open the Parent drop down list? Can you replicate the issue if you enter your site in safe-mode?