This hasn't happened since I got the watch at launch. I took my phone with me, as when I went out for a run/jog the watch said I should bring me phone with me for 20 minutes. I assume that's for some sort of calibration. Well I ran/jogged for 32 minutes outside, used the "outdoor run" setting in the workout app. When I get home, it says I only exercised for 18 minutes! So frustrating!