Hi Phil,
Just wondering if you’ve made any progress with this, particularly the 500 error. So far as I can see, in my case the only reason it reports a fast speed is because it produces a 500 error and does not load the real page in PageSpeed Insights. It does not cause any problems when actually visiting the sight, but I’d be concerned that somehow this will cause search engine crawlers to get loads of 500 errors.
Thanks