hello @CLOUD_PHT - welcome to Meta 
i assume you are running more than one website on the same machine configuration? (like a wordpress site + discourse)
the issue is that you are routing traffic through docker’s internal network (port mapping), which masks all incoming requests as the docker gateway ip (172.17.0.1). because internal nginx doesn’t recognize 172.17.0.1 as a cloudflare ip, it drops the CF-Connecting-IP header for security.
to fix this, you need to switch your setup to use a unix socket - this allows your outer nginx to pass the traffic (and the headers) directly into Discourse without docker’s network borking the ip addresses.
follow this official guide, and make sure you keep cloudflare.template.yml in your app.yml file when you rebuild.