Android node does not connect through VPN

My Android node (latest syncthing build) connects well when being in the same LAN. When connected to this LAN through VPN it does not see the other nodes. The announcement server is green OK. I can connect to the other node from the Android phone with SSH. What could be the reason for not syncing? How can I debug this?

Forget it: While typing this it connected - just took about 20 minutes. So have patience on VPN. :wink: