After one of the WordPress updates I started to have an issue with the text editor. Basically none of the features worked, and after saving a post in plain text the data was deleted.
I found a solution on this post: edit the file “wp-config.php” and add a line of code.
if ( !defined(‘ABSPATH’) )define(‘ABSPATH’, dirname(__FILE__) . ‘/’);//Add this line
define(‘CONCATENATE_SCRIPTS’, false );