Hi Guys,
First of all, we recommend keeping Cornerstone and X updated to the latest versions, although we are still fixing minor bugs, it should be working fine on your installation and not drastically failing as you describe.
If you want us to help figuring out what is wrong on your installation, please each of you open a individual thread, explain the situation you are facing in details and provide your login credentials in a secure note.
If perhaps you prefer to downgrande you can download the stability release
You can download it from your Apex Dashboard, the link is just below the theme download link
https://theme.co/apex/dashboard
To downgrade it, please follow these steps :
1-Revoke your License from WP Admin > X section and also remove it from your license page on Themeco.
https://theme.co/apex/licenses
2- Temporary disable any caching plugins and purge all your server cache.
3- Delete both X theme (/wp-content/themes/x) and Cornerstone plugin (/wp-content/plugins/cornerstone) by connecting to your FTP (your settings will be saved in the database)
4- Download the stability copy of X and upload it to your themes folder via FTP OR you can upload the x.zip via Appearance -> Themes section.
5- The previous version of Cornerstone will be installed automatically when you head over X tab of your dashboard. Now you try validating your X theme again and then try to install any other extension and it should function properly.
Let us know how it goes.
Thanks!
We are taking up to 24h to reply, so please bare with us.