I am running a RustDedicated Server installed via steamcmd, on a Debian 12.9 Bookworm VM (VirtualBox). I can connect to the server locally with the windows host machine and the local IP-adress of the VM (network adapter is bridged adapter). I can connect via client-connect <ip>:<port> commmand in the ingame console.

now I created a VLan using Zerotier and connected my Debian VM and my Windows PC to the Zerotier network. both are authenticated via the Zerotier Central.

When I try to connect via the ingame console using the Zerotier IP (that's the IP I get from sudo netstat -tuln | grep 28015. I also configured the Rust Dedicated Server to use this IP that is coming from the Zerotier network). I get the following error.

Rust Console 4.0
> client.connect <ZeroTierIP>:<gameport>
[EAC] Logging in with Steam ticket...
Found 0 server query results, attempting direct connect...
Connecting: <ZeroTierIP>:<gameport> (Raknet)
The referenced script on this Behaviour (Game Object '<null>') is missing!
The referenced script on this Behaviour (Game Object 'effect - FXAA') is missing!
The referenced script on this Behaviour (Game Object 'effect - FXAA') is missing!
The referenced script on this Behaviour (Game Object '<null>') is missing!
The referenced script (ModelViewer.modelviewer) on this Behaviour is missing!
The referenced script on this Behaviour (Game Object 'ModelViewerCamera') is missing!
[70.2s] asset_warmup_async
Disconnect Reason: Steam Auth Timeout: No auth response
Disconnected (Steam Auth Timeout: No auth response) - returning to main menu
got title filename: C:\Program Files (x86)\Steam\steamapps\common\Rust\temp\4be3b72150f231aee6fba12bcef8907f.png
Playing Video C:/Program Files (x86)/Steam/steamapps/common/Rust/RustClient_Data/StreamingAssets/MenuVideo/oilrig.webm
Failed to parse favorite server endpoint: eu staging.playrust
Failed to parse favorite server endpoint: ddddddddddd.rustoria.uk

somehow the steam Auth times out and I dont know why. I added all these ports to my debian VM's ufw and also tried to disalbed ufw entirely.

28015                        ALLOW       Anywhere                   # Rust server
28015/udp                    ALLOW       Anywhere                   # Rust server
28015/tcp                    ALLOW       Anywhere                   # Rust server

28016                        ALLOW       Anywhere                   # Rust server rcon
28016/udp                    ALLOW       Anywhere                   # Rust server rcon
28016/tcp                    ALLOW       Anywhere                   # Rust server rcon

27015:27030/udp              ALLOW OUT   Anywhere                   # Steam ports
27014:27050/tcp              ALLOW OUT   Anywhere                   # Steam ports
4380/udp                     ALLOW OUT   Anywhere                   # Steam port

What is causing the SteamAuth Timeout?