There is an unknown issue occurring between CloudFlare's cache and your origin web server. CloudFlare monitors for these errors and investigates as they occur. If you are seeing a 520 error
on your website, please pull the corresponding error log from your server and contact CloudFlare Support. Please include the Ray ID from the 520 error page. You can find the
Ray ID at the bottom of the error page.
A potential cause could be that your web server is sending a response header that exceeds CloudFlare's maximum response header size. This could be the case if you're sending an abnormally high number of cookies for example.