Tunnel works only when I browse to my URL including port number


I have configured a tunnel to my opnSense web frontend, which runs on port 8878.
In my tunnel I have entered as URL therefore. Unfortunately I can’t connect with this URL: https://opnsense.mydomain.ch. Error message is ERR_CONNECTION_TIMED_OUT. When I my Cloudflare WARP client and connect to the VPN, then the exact same address becomes working.
With WARP disconnected I can only connect to https://subdomain.mydomain.ch:8878 including port. Although I have already setup the port number in my tunnel.

I have also proxmox server, which is also running with https and on port 8006. I have created a tunnel for this server as well and there I can connect with closed VPN without entering the port number.

Now I’m a bit stuck. Why do I have to enter for the opnSense tunnel the portnumber but not for my proxmox service? Is there something I can check to isolate the issue?

Hi, I have a short update. I think, that the second tunnel had only worked without port number in my browser url, because something was cached. Now both tunnel behavior ar identical.

What I don’t understand is this. When I enter in the tunnel setup the portnumber. Why do I have to enter the portnumber also in my browser?