The Autoptimize plugin is great but it's known to break websites because of CSS and JS concatenation (combining of codes into one file) and/or minification. It's best that you consult with a WordPress website optimization service to configure the plugin for you. A professional developer is required to review all of the CSS and JS used in your site and he/she will decide if it's safe to concatenate all of the resources of your site.
Autoptimize caches minified resources so even if you deactivate it. The cached files might still be in use. Would you mind clearing Autoptimize's cache then deactivate it again? Please contact Autoptimize support for full usage instructions.
X and Cornerstone's resources should also be excluded from minification because they are already minified. For more details, please see https://theme.co/apex/forum/t/customizations-performance/210
You will need to contact Autoptimize's support to learn how to exclude all of X and Cornerstone's CSS and JS.