Hi Alina,
Thanks for writing in! Upon checking your referenced site, I see that you’re using an older version of X theme (6.0.4) and Cornerstone plugin (3.0.4). The latest version of X theme is (6.3.8) and Cornerstone plugin (3.3.8) as you can see on our changelog here (https://theme.co/changelog/). First I would suggest you to update your X theme, Cornerstone plugin and see if that resolves your issue (https://theme.co/apex/forum/t/setup-updating-your-themes-and-plugins/62).
If you’re still having issues, then I would suggest you to disable your child theme temporarily by activating your parent theme and see if the issue related your child theme customizations.
If you’re still having issues, then I would suggest you to disable all of your 3rd party plugins except Cornerstone plugin and see if the issue is related to a plugin conflict. If the issue is resolved, then you can activate your plugins one by one to see which plugin cause the issue.
Also when testing, if you’re using a caching plugin on your server, please make sure to purge your server cache and also clear your browser cache before testing.
Let us know how it goes.
Thanks!