DON'T CHECK "USE EXTERNAL BLUETOOTH GPS" under motorlap options, keep it off / unchecked

If you wanna be sure you anntena it's working, go to race screen (where chronometer and that) pick up you antena with one hand (and phone with the other) and move the antenna fast to multiple directions, you will see changes in the speed

So let me get this straight, in order to use an external GPS unit you need to uncheck the option labeled "Use External Bluetooth GPS"? Very intuitive.