I believe the cause to be closing the window when you open the recently used apps at the bottom left of your phone. It fixed for me until I closed the window again, causing it to stay at zero energy.
I think that's the cause too! I had no issues before I closed it from my recent apps.
Yea I've had the same problem twice now first time it fixed itself after I reopened it. Second time (atm stuck still) it hasnt fixed itself, if anyone has a fix please tell.