Same problem to me - yesterday I did a skitour and the first 10minutes the heart rate was about 20-25 beats lower than my real pulse.. i stopped the measurement and started again - same. after the 10mins the HR increased suddenly to a credible pulse.. till the end of the tour it was ok. I can´t say, if the problem started with the last update - but, like many others of you confirm, previously it worked MUCH BETTER!! .. so garmin do your job and fix it pls - it really annoys me and I am not happy with my 935 at the moment!!!