May I ask what error do you get when you try to access WP-admin?
Only the 522, but for the admin, or generally for the whole Webste?
Kindly, do a re-check regarding the SSL settings and cookies at your origin host/server.
- Do you have an valid SSL certificate propperly installed at your server which covers your naked domain and any other sub-domain(s)? → Was the Website working over HTTPS before moving to Cloudflare?
- Is Cloudflare allowed to connect to your server? → https://support.cloudflare.com/hc/en-us/articles/201897700-Allowing-Cloudflare-IP-addresses
- For the SSL, may I ask what kind of SSL option have you got selected under SSL/TLS tab on Cloudflare dashboard for your domain? (Flexible, Full, Full Strict) → Deprecated - Step 2: Setting up SSL with Cloudflare
May I ask have you contacted the support of your hosting provider? What did they, if so, told you about any outages or some incidents?
May I suggest looking into below articles: