WP Post Editor Page Messed Up

If deactivating the plugins and moving to a default theme didn’t work, my next step would be to reupload the WordPress files.

Have you tried:

– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.

– re-uploading all files & folders – except the wp-content folder and wp-config.php & root .htaccess files – from a fresh download of WordPress. Make sure that you delete the old copies of files & folder before uploading the new ones.