Mega Menu Categories are disappearing

I went through the forum and looked at everything related to mega menu, but nothing could help.

My site is http://www.fireinvestigatordirectory.com

I am using the Mega Menu, because I have hundreds of categories. When I created the “Structure Fire” mega menu everything went great, and let me have 4 subheadings with 10 – 15 entries under each one. It was simple to set up and worked flawlessly.

However, when I am creating the “Laboratories” mega menu there seems to be a maximum limit on what I can put there. Every time I try to add 9 sub categories under “Northeast US” it keeps deleting 6 of the categories. (when looking at post categories, the categories are still there, and do show up in the categories in the Menu page.) I can add the 6 additional categories in the menu creator screen, and when I click save it 1.) removes the last 6 categories from the mega menu again like I never put them there, and 2.) unticks the Unfold Main Menu. In fact wordpress removes what is considered Menu 1, which this menu is under.

I have removed the 3 plugins I had, and nothing changed. I tried to resolve it by using the different Header options. Enfold theme says it is up to date. Is this a common problem, is there a workaround, is many categories and sub categories not appropriate for this Mega Menu, is there a maximum number of categories that can be used with Mega Menu? What do you suggest. By the way….awesome theme.