Update I added a new option to ConnectStats to mitigate the issue

I started noticing something quite weird with the activities recorded on the Fenix 3 since I updated to firmware 6.5 for my running activities. The pace reported on garmin connect is quite off, while the pace of the splits seems correct. At the very least the two are very inconsistent, the pace on the pace graph is typically quite slower than the correct pace. You can see an example activity here, all the lap pace overlay are clearly toward the minimum of the lap pace, which is not possible.

While if I look at a similar run but in december (pre 6.5) it’s much better

Looking at the activity on garmin connect, shows the same issue, so I don’t think it’s a bug in Connectstats (my initial thought). Old activities (pre 6.5) do not show the issue. On Garmin website, while it’s harder to see, if you move around the pace, you can see most values are quite slower than the average pace for the activity.

If I looked at the same activities on Activity on Strava,  the graph is consistent with the splits. Strava seem to recreate the pace from the GPS points (my guess).

I then looked at the details in excel, here too, it’s quite clear that the speed recorded for each point is quite slower, while the speed of the split is correct. For example for the first split, I looked for the 1000m point, computed the time to start 308 seconds, which gives 3.24 meter/seconds or 5:08min/km. While a simple average of the speed recorded for each point gives 2.72mps or 6:07min/km. The simple average is inaccurate, it should be weighted by the time between points, but this is way off.