Wrong Elevation Gain in the Fitness app on Watch 6

After receiving Apple Watch 6 last week I have noticed that Elevation Gain in the Fitness app is very wrong. On all 3 training runs it has been less than half of what it was with Apple watch 4 doing the same runs. And I'm quite sure that Apple watch 4 is more correct!

The altimeter is working fine. I have watched the altitude about every minute on my runs, and it seems to be correct. It's just the gain that it's not able to compute any more. It seems that it doesn't accumulate small changes. Part of the course, about 2km, went up and down all the time, just small hills, each maybe less than 1m altitude difference. At the end of the 2km the Elevation gain was the same as at the start. Not correct!

I have exported the data from the same runs with Watch4 and Watch6 and made a graph of the altitude data. They are very similar. So the altimeter seems to be correct, it just can't compute the gain!

I also have a Garmin Fenix 6, and it gives Elevation Gain very similar to Watch4! If I import the run from Watch6 into Strava, it also gives Elevation gain more than twice of what Watch6 does.

To me this seems to be a software problem on Watch6 (or OS7). Have any others experienced this?