Apple Watch 3 turns off on its own.
I have had this happen twice in the past 3 months. Just past the 6 mile mark my watch shuts down as though the battery has died. I can restart it and it will stay on for less than 2 minutes and it shuts down again. At that point in my run the battery is typically at 40% if I have cellular turned on. Once I end my run it works fine from that point on. I use the Strava app. Today was light rain and 40° the last time was dry and 30°. Both runs were identical and the watch shut off at the same location. I started the runs at full charge. I listen to music with AirPods.
Apple Watch