I use to check my websites with WebPageTest quite often, to check if everything is working fine. I never had problems with Wordpress sites I run, but the Prestashop site I created is driving me crazy.
While it’s working fine, and customers are buying, when I try to test the performance, very often (not always) I get Error 500 results like this one from today: http://www.webpagetest.org/result/131205_E0_M4V/
As far as I know, the site is performing well for humans, but WPT doesn’t seem to like the site.
I the site I have a plugin that redirects the user to a specific domain, depending on the browser language. Maybe that’s the problem? I’m trying to avoid it adding the /en/ folder for English language, but the problem is still there. Any clue? Is anything wrong with my site?
The Kansas City location connected to 108.162.196.50 while one in Israel connects to 108.162.197.50 and gets a 500 error (this is also the IP where I end up, probably the Amsterdam node). Have you tried temporarily disabling CloudFlare?