Cloudflare can only proxy traffic going over the following ports listed below. If your traffic is on a different port, you should create a subdomain for that record and then add it as a record in your Cloudflare DNS zone file as something we don't proxy (gray cloud = no Cloudflare proxy or caching on a record).
For requests made via HTTP:
For requests made via HTTPS:
On the pro plan and above, traffic on ports other than 80 and 443 can be blocked using WAF rule id 100015: "Block requests to all ports except 80 and 443".
80 and 443 are the only ports for HTTP/HTTPS within China for zones that has "China Network" enabled.
80 and 443 are the only ports for Cloudflare Apps to be able to proxy on.