If you have tried everything in the linked article, contact support with a RayID of a 521 and they should be able to track down what went wrong.
To contact Cloudflare Customer Support, login & go to https://dash.cloudflare.com/?account=support and select get more help. Please give Support the complete details and link to your Community post. Here’s a bit of background on Cloudflare Support for reference:
https://support.cloudflare.com/hc/en-us/articles/200172476-How-do-I-report-a-bug-to-Cloudflare-