Hey there,
we are using something like described here:
https://www.mavention.nl/blog/building-global-navigation-sharepoint-2013
to manage the global navigation. It worked.
But from one day after the other it stopped working for the normal users. The farm admin can still see the navigation. So i thought it has something to do with the permission. We changed nothing.
I can read with a normal user from the managed metadata. Eg using it to tag a document.