Glad to hear the issue is solved (more or less) Basically there shouldn't be an issue when using a VPN, but of course this always depends on how it's configurated and how the traffic gets routed exactly. Maybe the HIVE port (6001) does not get routed properly?
I don't think it's related to Steam btw, since we're not using Steam's infrastructure for networking (although on some distros Steam uses its own libraries, which can cause trouble when you're not using Ubuntu - but I don't think networking is affected by this, at least I haven't seen any issues related to that yet).
What about the server list? Are you able to see servers when using a VPN? The server queries do not get routed by our HIVE, so when querying a server, our servers are not involved at all. You only get the full server list (a list of all IPs) from our servers (apparently this worked), but then the game queries every single server individually
But as mentioned, since there is a timeout of 1000ms for server queries, you may hit this limitation if the pings are high, especially when using a VPN (the hive login, on the other hand, has a timeout of 30000ms).
Nevertheless, we want to rework the way how the game communicates with the HIVE anyway. Right now the game uses a socket connection, but in some rare cases this causes trouble (e.g. sometimes antivirus programs prevent the game from establishing a loopback connection, or - especially on Windows - some sockets are misconfigurated etc).
The new implementation uses a simpler approach which is much less error prone (it shouldn't be affected by a VPN or NAT), I pretty sure this will solve this issue. I guess this change gets implemented in December (after the next update).