I've been getting abnormal heart rate alerts while seated where the 745 optical heart rate sensor would report 130-168. During these periods I strapped on my old 935 which reported 56-65 on its optical HR sensor because I was getting worried that there could be something wrong with me physically. I also tried to measure my pulse with a finger on my carotid which tends to agree with the 935 HR readings.
The 745 has been giving these crazy alerts about 3-4 times per day in the past week.