Thanks for your detail info. I just try to replicate your issue above on my localhost server. But seems it just works fine on my side. Please check this image: https://www.dropbox.com/s/lyli1j5k5gkmnd7/192.168.1.169_staging_wp-admin_post.php_post%3D4%26action%3Dedit%28Laptop%20with%20MDPI%20screen%29.png?dl=0. Anyway, did you get any error message on backend editor when that problem occurs? or can you try to enable WP_DEBUG?