I was quite happy to tell them about this thread and how there are at least a hundred people on this thread alone talking about it.
My watch is still better than it was, but it has gone back to being less reliable than it was. My biggest gap so far is 60-90 minutes.
The behavior is more consistent now with what others report on there. It is *more* accurate when I am not moving, and will not monitor AT ALL while moving unless the glance or exercise app is running.
From a strictly technical perspective it seems as if they adjusted the scheduled task which would run the heart rate monitor checker. Because when the glance or exercise app is up it is flawless. It just won't turn on as advertised periodically anymore.
To me it seems they adjusted how it looks for idle activity to see if it has spare cycles to check for a background heart rate, and they have now made it too sensitive and it thinks its always too busy if you are doing anything.