I wouldn’t really know what to look for.
If it were a GP related issue, this website you’re currently on would be doing the same thing. I would also be able to see it happening on your site, which I wasn’t able to do.
Do you have another server or a localhost (XAMPP for example) where you can install a fresh copy of WP/GP? I would be interested in knowing whether you get the same thing happening there.
Here’s a site for you to look at – completely bare: http://speedtest.generatepress.com
Does it happen?
Did you get a family member or friend to check out your site on one of their computers using Edge?