A 500 internal server error indicates an issue directly with your server. Please contact your hosting provider for assistance.
Usually this happens when an origin server has encountered an unexpected condition and was unable to fulfil request. A blanket error message for any internal errors that prevented the origin to fulfill the request and were not caught at the origin.
In the very rare event that an exception throw with Cloudflare’s edge or an internal DNS timeout occurred, Cloudflare will return a 500 with the page stating "cloudflare".
If you don't see this, the issue is occurring at the origin server and you'll want to work with your hosting provider on the issue.