Reviving this thread because I'm having a similar problem...
Running on stock, rooted.
It happens often enough for it to be a problem.
Only concern is when I go to sleep and rely on my phone as an alarm clock. I need my phone to work
Please note last charge cycle on the attached screenshot. Battery was at 84% and completely dead after sleeping for 8 hours. It doesn't even show me how the phone died, or what made it die.
During the day, I think I have the same problem. My phone will simply not turn on at times. I have to do a battery pull before I can get the phone to turn on again.