Did you get an answer to this? I am also getting this disconnect with GPS, pace, and distance. I have used the Rival watch since January, with no problems (except the optical HR, which I find too inaccurate to be useful). It was tracking rides and runs nicely, including showing pace and distance. A few days ago, at the start of a run, it buzzed to show I had a GPS signal, but as soon as I started the workout, it showed only n/a for pace and distance. The little map on the watchface showed my course as I ran, but no pace or distance data came through. The same happened the next day on a ride. I stopped the workout after a kilometre, started it again, and the same thing happened: n/a for speed and distance. This is in a country town, with decent GPS coverage, and on courses that the same watch was able to track up to a week ago (and my previous Polar always tracked). I have read all I can find on this, with no success. I am not running and riding through jungle, tunnels, between tall buildings, or miles from civilisation. These are open roads in a decently populated part of France. I’d love to find a solution to this, because it is deeply frustrating.
Are you sure the GPS module has not crashed? This happens to me on a regular basis and the watch utilizes solely the acceleration data to calculate distance and speed.