Charge 5 inaccurate heart rate detection when exercising

[gl661]

I used to have a Charge 2 which was much better, but after upgrading to a Charge 5 my heart rate recording during exercise has been terrible. I have a daily routine of walking half an hour on a treadmill at 3.2 mph at a 15% incline. It gets my heart into the 155 to 160 bpm range. It is a very steady intensity exercise.

Charge 5 has logged my heart rate accurately only once. Out of about 50 attempts. And here is how it looked.Other attempts look like this.

As an engineer, I know a little how this device works. So I tried putting a sleeve over the Fitbit while exercising so all ambient light was blocked. I used a rubber band and placed the Fitbit over my bicep while exercising to reduce shaking. I even tried putting it on my side above my hip to get rid of virtually all shaking and ambient light. Nothing helps.

Based on the graphs it appears the problem is in the "smoothing" algorithms used for Charge 5. What's going on? Why was Charge 2 so much better?

Moderator edit: clarified subject.

[Vintagedad]

My new charge 5 will not pockup my pulse. My charge 2 did. Now what?vintagedad