Thank you for the clarification, don't worry about the Cornerstone validation because that will be resolved once we address your issue with X.
Your real issue is this, your version of X and Cornerstone is not compatible. Your Cornerstone (3.0.4) is up to date, but your X (4.3.2) is not.
Most likely the automatic update method won't work with this outdated X, so you need to do the Manual X Update Via FTP guide that was provided here (you can also do this via cPanel's File Manager app). You can download a latest and clean X .zip file here.
Please be sure that your x folder is named x (not x-2, not x/x, etc.) or else the Cornerstone won't honor it and will ask for validation.
Remember to clear all caches (plugin, server-side, CDN, and browser's cache) after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Let us know how it goes,