I have two phones. Strava works just fine on one of them. It used to work on the other as well, but sometime last year, I noticed this bizarre behaviour, which continues until now.
If I press the big orange round button, the screen with time, distance, and speed in giant numbers shows up. As long as auto-pause is turned off, the time ticks away, while the distance and speed remain at zero. If I go to the screen with the map, it shows my location reasonably accurately, and shows the little blue dot moving as I move. Upon finishing the activity, a map of the route, quite accurate, appears, along with plausible values of distance travelled and average speed. However, during the activity itself, the distance travelled is zero and the average speed is zero.
If auto-pause is turned on, the clock ticks for a few seconds, then auto-pause activates, whether I'm moving or not.
If I leave the Strava app on my other phone, a blue strip appears across the top of the screen, indicating that Stava is using my location. This has stopped appearing on the problem phone.
I tried removing the app and reinstalling, it didn't help at all.
Hardware is iPhone 6s Plus, most recent version of iOS.
Any thoughts?