I already raised this question some time ago and John answered that there is no point in keeping location service on (and record gpx) when, let’s say, screen is off, since majority of hw will kill the service. Fair enough, this is the decision of the developer.

I only can say that, at least to me, to record gpx while screen is off is crucial when I don’t have external power for the phone (on my dirt bike) and battery, late in the day, is running low. In these circumstances, sometimes I know where I am going and don’t need to keep the screen on, but still I want to record my track (I turn off the display, to preserve battery and I am still recording in the background).

Now I am using additional little app just for that in parallel, which is not elegant, but still is a solution. I would prefer that dmd2 records in the background, though. But, ultimetely I respect the decision of the developer.