@jandur: The user manual suggests that your tracking values may not be accurate in the following instances:
- If you stop swimming before reaching the end of the lane
– If you change your swimming stroke midstream
– If you stop moving your arms before reaching the end of the lane
– If you kick with your legs on a kickboard, or swim without moving your arms
– If you do not pause or restart the exercise by pressing the Back key, but finish the exercise by pressing the Back key and tapping FINISH
If the above isn't applicable, try manually starting your workout to see if this helps. If you already do, enable Workout Detection for swimming to see if the results improve (Samsung Health > Rotate the Bezel > Settings > Workout Detection).