TB Megamenu 3rd level does not expand
TB Mega Menu is a pretty awesome module, but we've been using it for a few years and occasionally run into issues where the rendered menu doesn't appear to reflect the menu's structure. It gets "stuck." Here are a few things that have worked for us, in various combinations:


Clear your site's cache.
Rebuild your site's menus (use devel for this).
For the items that aren't showing, create a new parent menu item and move the child items to under the new parent and delete the old parent menu item.


From our troubleshooting, we've determined that TB sometimes seems to "lose track" of the menu and basically all of these efforts are intended to get TB to re-sync.

Hope it helps!