One thing to check is whether you have any out-dated plugins. I had a similar issue where the advanced layout editor did not load. I checked the browser console and saw a Uncaught TypeError: jQuery(...).live is not a function error. This lead me to this posting: https://stackoverflow.com/questions/63481440/fixed-wordpress-site-uncaught-typeerror-jquery-live-is-not-a-function-cau

I removed the out-dated plugin that was responsible for the error and the advanced layout editor loaded up.