Overlay burger menu not showing on most pages

[dabu]

I installed the overlay burger menu, but it only works flawlessly on Firefox (neweset version, Macos).

On Chrome, Safari and on my iPhone the Overlay burger isn't positioned floating on the top right, but it gets displayed at the end of the page content. Strangely on one of the pages it works correctly (https://tonhalle.at/kurse/), but on all the other ones it doesn't.

I have to say that there are two overlays on this site, but they both don't work where they should.

Could you please help me @arminunruh ? Thanks a lot!

Attached:
first image: how it should look (and how it does on Firefox):

second image: how it looks on Chrome, Safari and iPhone:

[dabu]

Ok I found it out myself, sorry… 
But for anyone else having this problem: It was the plugin "WP fastest cache", I had to delete cache and mimized CSS (both!), now it works on all browsers and iPhone.

[arminunruh]

ah ok very good!

yea its always good to try these steps!
have a great day