A few days ago I set up a Cloudflare tunnel on a dedicated Ubuntu Server VM to remotely access Proxmox.
I can log in without problems, but when I try to turn a VM on or off it gives me the error "Connection error - server offline?". I can only see the statistics on "Summary" and the VM on "Console" with noVNC.
I can't even open the Proxmox shell when I'm connected to the Tunnels.
Do you have any ideas?

I had this issue and found it was a problem with the web blocking on my work's network. Call to explain that I wasn't doing anything nefarious and it works again after whitelisting my public hostname.

@tilimirti did you able to resolve the issue? I have the exact problem

@tilimirti did you able to resolve the issue? I have the exact problem

Yes, it was a firewall issue where it was blocking my public hostname on the network I was accessing from.

I'm facing the same problem and i have ports allowed 80,443, 8006, and 5900 but still I can't access from my URL domain it's working perfectly from the local IP

i recently encountered the same problem.

1. check all ip used by all lxc and host (ensure no conflicting ip)
2. check the logs of the cloudflared lxc (tunnel logs)
3. checked dns, i enabled dns for ipv6 but the lxc cannot reach. hence, the error occurred.
4. updated the lxc to only use ipv4 dns
5. problem solved
6. monitor the ping status, and all seems good