GP hooks timeout

The error you've reported is a WordPress/server error - it's not caused by the theme.

XMLHttpRequest cannot load admin-ajax.php due to access control checks.

That's what you would report to your hosting support.

We know it's not a GeneratePress issue, as pages of results pop up when you put that error into Google - all people who are likely not using GP. If it were specific to GP, we would have hundreds of reports in our forum here.

I don't have a solution for it, as I'm not a server technician - I am however trying to help you find the solution by searching around and giving you snippets to try. For errors like these that are server related, that's the best I can do. You're much better off actually talking to your server technicians, who will likely have a solution that will work for you.