all the sites run GP for several years now and are on different servers. I don’t want to deactivate plugins there. sorry. all use sticky primary navigation and slideout menu.
Problem can be eleminated by deactivate slideout. But I have more sites Like this with the same behaviour. Happened first with 1.6.x
added the snippet to several of my sites into the functions.php manually and the slideout nav is back. But the to top button is still gone away. The button comes back when I deactivate nextgen. Hope you find a way to come in contact with nextgen.