I think MS intends to clarify the confusion in waves
Try a hard reset on it.
New firmware hasn't resolved sleep issues on mine. Put it to sleep earlier, after about an hour later went to wake it up, and got the black (off) screen. So no worse, no better.
It did seem to correct battery meter percentage coming out of sleep (used to always revert to 100%), but it's only been less than 24hrs so I'll wait and see if that bug has finally been squashed.
That's interesting, my experience is exactly the opposite - sleep issue seems to be fixed but battery meter is still broken.