I threw down 11 short runs of a section of downhill at the local. I record with my phone and Garmin but only upload from the Garmin.Which device are you using? If you say a phone you’ve answered your own question.
I did 5k miles of cycling last year, all with Strava and all with a Garmin gps. It might not be entirely accurate but it is absolutely consistent. You have to make allowances for GPS or satellite coverage but that’s not a fault of Strava.
The runs were all about the same with times between 1:26-1:31 but one recorded as 4:11 and that was on the Garmin. The phone times were not going the same but within a second of the Garmin times.however the 4:11 was recorded as 1:31.
Another ride of 65km recorded I had done 1123km and traveled at atop speed of 936kmh but that was another Garmin device I once had. Oh and the phone also at times records funny data.
Consistent it ain’t that’s for sure. Sometimes it’s dam right unstable.