I have been running into persistent issues trying to use Cloudflare with a domain running Wordpress.
At my host’s request I have tried every possible option in the SSL settings. It simply changes the Error ID that I receive.
At the moment, it’s showing up Error 520. They have run out of ideas.
The error seems to trigger whenever I attempt to upload a file to the media library. Strangely enough, the frontend is unaffected during this period — only the backend redirects to the CF error page.