Apple watch 5 running distance

I ran a marathon 2 months ago with my apple watch 5 gps + cellular and tracked the run using the native workout app, and the watch overestimated the distance, showing 43.34km

I reset the motion and calibration data again and calibrated the watch over the last two months (I used only the native workout app).

My second marathon with the watch again came inaccurate, showing 43.46km

Both courses were flat, and my health profile data is up to date.

Any ideas what is wrong?

Thanks