I'm trying to set up a managed metadata navigation based on a term store for my site. I can create as many levels as I want in the term store, but only top-level terms appear in my navigation. In navigation, each term is set to Simple Link or Header. Whether my header is empty or has a link, no drop-down list appears below it when I hover over it or click on it. The publishing feature is enabled on my site. This is a SharePoint Online site (O365) that has just been migrated since SP 2010.