Hello @kludrik,
Thank you for the very detailed post information. I have logged and investigated the issue. It turns out that the out dated Rev Slider were causing the issue. I have temporarily remove the plugin so that you can login to the dashboard. I also noticed that your X and Cornerstone were outdated. Could you please update to the latest versions? Our latest versions are:
- X theme
7.2.3
- Cornerstone
4.2.3
This latest release contains fixes for several issues so be sure to check out the changelog (http://theme.co/changelog/).
To learn more how you can update X theme and Cornerstone, please check this out:
After doing the updates, always remember to clear all caches (if you are using WP Rocket, WP SuperCache or W3 Total Cache) when updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Please let us know how it goes.