As mentioned in the 3rd post of this forum … I’ve use the order field. It sorts them correctly in wp-admin …. just not on the page.
I don’t know how to help with the categorically nested forum issue you originally posted (didn’t even know you could do that), but regarding the Order issue…I just struggled with it and found that you must Order every forum you create numerically (if you have 40, then they must all be numbered 1-40). As the default number is 0 for a new forum, it will automatically be ordered at the top (0-40) unless you designate it with another number. Hope this tedious little solution helps you in any way!