Simulator vs real device

I've mostly been developing my app (for the Edge 530) on the simulator but took the real device out for a spin today. For some strange reason, I got the values for current/average power fine but current/averge speed and distance didn't show up even with an active session (and GPS OK). My app has pretty much all permissions you can image since I sideload it anyway. The data shows up fine with simulator random FIT data. Any theories what could result in 0-data for speed/distance? GPS not active, after all?