Mike B 
Headed out for today's 14.1 km walk with bated breath. Would today be the day that the old ticker sends me to the doctor? Well, no. About the same speed at 9:21 per but the heartrate was down to a moderately light 100 bpm (67%). The mystery abides. It was a gentle 11.7C with 71% humidity.
Other than that, I got nothing.