Changes only shown in customize / Broken icons when logged out

Hello,
I made changes in the customizer, which I saved, but the changes doesn’t show afterwards, leaving the customization. When I’m logged out of the backend, the changes also don’t show and the “search” and “back to top” icons are broken. (I cleared the cache several times.)

If you wish, I can send you screenshots.

All the best, Volker

The page I need help with: [log in to see the link]