Apple Watch 3 gps is not showing distance and in open water swim mode - what can I do?

Hi, my new apple watch 3 (gps only) is not showing the distance and avera pace while swimming. It is only showing the timer and burned calories. Once synchronised with the app, I can see my exact swimming rout in the app/map. Everything is working very well in the other training modes such as running, etc. Is there anything I can do? I already updated, unpaired and restarted the watch, but it is still not working.

Thanks for any help!