Can't Connect to Teamviewer when Mobile Phone Tethering

I'm having a problem where I connect to the internet using my mobile phone hotspot - TeamViewer won't let me sign in. If I switch to WiFi then I can log back in fine. It's ok most of the time but when I'm on the road it just doesn't work which is frustrating. Any ideas why it won't connect to TeamViewer when tethering? All I get is not ready check your connection.