I walk on a treadmill every morning, pretty much the same speed and length of time every day and my Series 3 had been pretty consistent in terms of exercise minutes - 40 minutes on the treadmill results in around 36 exercise minutes, for example. But the last two mornings, fewer minutes were counted as “exercise” - just 22 yesterday and 9 today. The distance measured is consistent with previous measurements. I restarted my watch after yesterday’s low measurement (I do that about every day anyway) but it was actually worse today. Watch o/s is current. Has any one else experienced anything like this? The watch, of course, is well out of warranty.