It's actually loading but there are times that your site is a bit slow, even by installing a plugin took longer. I also tried fixing the HTTPS URL which took a while using Better Search Replace plugin (68 tables) and it works on the live page (no more CORS issue), but in the builder's preview, it still displays the CORS issue.
Perhaps your hosting has passive caching? Cache plugin is inactive and I also override it through wp-config.php so there should be no caching.
I also deactivated the plugins and the site is still too slow, and I noticed it always display "waiting for available socket" in the browser status bar. Perhaps your site is getting more traffic? Or is it a shared hosting? Else, would it be okay if you set up a staging in a different host environment separate from your current one?