Open water distance tracking on Apple Watch inaccurate and inconsistent

Apple Watch S10 with WatchOS 11.5

Did a few 1km open water swims, getting weird distances from the Apple Watch workout app. The first swim was tracked 570m (about half of the actual distance), the second one tracked only 200m (i.e. only 20% of the actual). The map on the iphone Fitness app does not show any gps tracks, but on the Withing app (synced with Apple health), I can see some locations from my workout (see screenshot below)

Any tips how to improve accuracy? Why doesn’t it use the gps locations tracked to calculate the distance (connecting the few dots tracked would provide a highly more accurate estimate on the distance).

[Edited by Moderator]