I deactivated all plugins except theme4press core and redux framework but the issues is still producable, maybe not as extensive as before (I am not sure about it).
Anyway, my concern is that it has something to do with the gap you can see between the menue sublevel (like ‘Beiträge’ -> ‘Ausstellungen’) and the subsublevel (like ‘Ausstellungen im Flur …’). You can check on my test site test.gfcev.de. Hovering across this gap frequently causes that flicker.
Is it possible to position the subsubmenue slightly overlapping or directly adjacent to the submenue, so that there are no gaps for certain?
I would like to test this!
Thanks and best regards