Aegaeus not responsive acc. to Google or iPhone

I have been happily using Aegaeus for some years now and recently found out that Google mentions that my site (www.drentsheerlijk.nl) is not mobile-friendly and this also impacts my SEO. I have always had the responsive styles switched ON and when I scale down on my pc to a smaller window, it all scales down too; top menu changes to the drowndown version and all seems responsive.

But the Google analysis does not agree: https://www.google.com/webmasters/tools/mobile-friendly/?url=drentsheerlijk.nl
Result: Not mobile friendly

And I also noticed that my site does not scale correctly on my iPhone.

Switching the Aegaeus option OFF>ON again does not help. What can be done to resolve this?

best regards,
Martin Meerman