@wotus After several unsuccsessful tries I found a workaround forcing the watch to measure and record the temperature in openwater swimming (basic and custom exercise), with which all other exercises have no problem.
The only way I found is to activate S+ Weather - Insights before the start.
But even then, the realtime temperatur data field shows no value “–”.
Only if I switch the display to the Weather screen and then back to my first view, the real temperatur value will be shown and appears then in the logbook and in SA.
Can someone confirm this strange behaviour of missing temperatur in openwater swimming which didn’t happen before the last firmware update?