Cloudflare 502 in Wordpress

Do you get a 502 in wordpress whenever a form is submitted?

I got them all the time submitting posts or pages. The link below offers a fix, but it doesn't say "exactly" what the problem is. But it does seem appropriate that an admin shouldn't be cached!

 https://support.cloudflare.com/hc/en-us/articles/200169526-I-get-a-site-offline-error-message-trying-to-update-a-WordPress-plugin-What-should-I-do-