I think I know what’s going on here because I came across this before.
Your site is not loading for me now, but when I looked yesterday I noticed that the menu uses the same class names used here:
The menu on https://discourse.pi-hole.net/ uses very, very similar styles - although the classes are different. Essentially all of these sites are using some variation of
on both desktop and mobile, which I believe is not the intended use for that customization. I think it’s meant for desktop only since mobile has no space for menus in that area.
I’m not really sure how this ever worked on your site in the mobile view.
You have a few of options:
modify the code to make it responsive (not really worth it as you’d only be able to show one link tops due to lack of space)
move the customization to desktop tabs in your theme.
use one of the supported theme components I mentioned here