Just notice the issue is occurring only when a page is published and page editor screen has some metaboxes. These metaboxes can either be from some plugin(Yoast, CMB2 or ACF) or from theme files.
In my case, after I update my website to version 5.1, preview functionality is not working. If I deactivate Yoast plugin then the preview functionality works fine. But I can’t keep yoast deactive, need a solution with which preview work with all plugins.
