This is an issue with some routers returning weird info when asked for their UPnP details. Either it doesn't return anything and the game sits there waiting until it does, or it returns malformed details which blow up Blockland.
You can try starting a server and leaving it frozen for about 5 minutes, It should reach a timeout and just continue starting the server. This is an issue with your router though - and v15 allows you to disable UPnP so you can host via the port forwarding method only as before.