Perfect track but 500m shorter of 15km run

Can't see the activity but why race on GPS only? Unless your racing a 30hr race, or start with a battery of like 10% that makes no sense...

Is this the race you're talking about? Then GPS only might be the culprit, also a quick revert might not help but can't explain that much.

You did wait for the signal to go green? Sure the actual run was indeed 15k?

Anyway, hard to say without the activity. Also, the garmin connect link would be better because strava does it's own smoothing as well.

Unless you're away from home, there's no need for battery saving measures like this.  I'd change the settings so that all of the GPS settings are enabled and the one to record once per second to get the best accuracy.

The watch will last for days without charging - it's not like an Apple Watch that will die after 7 hours of GPS based workouts.

We can't see your Strava activity unless you change your privacy settings on Strava so can't comment on that aspect.

I correct the visibility on strava, now you can see it. I will change settings only on 100 milers. The setting are on 1 second, and All systems, I wait go get gps lock before go. The problem is that this happen for second time. Perfect track, but crappy average pace and wrong distance.

I still see "The requested activity could not be found" when I click on the link.

Can you check now?

That works.  The thing that I noticed is that you have a 100m climb and descent.  I wonder whether your watch is taking that into account or not.

If you have a lot of climbing in a run, enabling 3D Speed and 3D Distance may help.

True.  VelinDilov  Read here for more information.

Tips to Improve Activity Speed and Distance for Forerunners | Garmin Customer Support