Heart rate sensor not working as it should

I'm using my AW since July for outdoor walking and indoor rowing. The readings of the HR sensor are inaccurate and insconsistent. Upgrading to watchOS 2.01 did not help

- very often the sensor delivers a HR reading only 2-3 minutes after starting the exercise

- very often the sensor looses contact during an exercise

- very often the sensor delivers readings jumping by 40 heartbeats from reading to reading

The sensor is also not accurately during normal activities over the day or when sleeping. The readings jump by 20-40 heartbeats although there is no change of activity.

I have purchased a bluetooth chest strap which gives during all activties reasonable readings.

I have changed the place where I wear my AW from left to right arm, up and down and I have also changed how tight the AW fits. I have even shaved my hear on my arm. But I had no success.

I am deeply dissappointed.

Any suggestions?