Thanks for sharing, @philipp_halla.
@manomano11 and @mchll9898, time out issues are mostly caused by third party scripts running along side the theme’s, Cornerstone’s and WordPress’ scripts. If your server, computer, internet connection or anything involved in the network can’t handle the request, it will throw out that error. What causes this specifically? I could not say because there are lots of factors you should take into account. For us support, we need to drill down between your host and X / Cornerstone first because there are host that have really slow servers and that causes issues.
@manomano11, since you said your setup is bare bones (fresh install and no plugins), you could first try contacting your host to increase your allocated memory or do it yourself by adding this code in your wp-config.php
define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );
Also contact your host to increase the max execution time to the highest possible value.
If it still doesn’t help, please test other web hosts. Some of them offer free trial or money back guarantee so you could test what works. You don’t need to move your site for testing. You can use a free domain like dot tk.
If you want a detailed guide on web hosts, please see this article from X Theme Tips.
Thanks.