I also have the same issue. I love this plugin and hope this can be fixed.
After some investigation using the developer console in Chrome I se it comes an error by just adding a picture from the media library into a page.
Error message:
POST https://<domain>/wp-admin/post.php 404
and
load-scripts.php?c=0&load[chunk_0]=jquery,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,moxiejs,plupload&ver=5.5:4 POST https://<domain>/wp-admin/admin-ajax.php 404
Based on this i found a post on stackoverflow that might can help. One user found out that the application ModSecurity treated this POST request as a potential threat: stackoverflow
