problem with front- and backend

Good Morning,

we had to move our domain to a new customer account. From Hosteurope to Hosteurope. Domain, database and WordPress were also moved.

I have now been able to fix all errors in the Debug.log and the WordPress and frontend can be called up again after the error message “a critical error has occurred”.
The frontend looks strange now. The content and images are displayed. Headers, footers, spaces, etc. are not displayed correctly.

Now the problems arise:
1. Customizer cannot be called (Blocksy Theme).
Even with Twenty Nineteen it can only be called up to a limited extent, since the Customizer is opened completely without style elements and therefore cannot be used.

2. All pages are created with Elementor. As soon as you want to edit the pages with Elementor you walk to a white page. Unfortunately, Safe and DebugMode do not show any errors.

I have already tested reinstallation of the plugins and theme, unfortunately without success. Does anyone have any experience or ideas on how to fix the problems?

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