I had a new problem yesterday 
I shut down the phone with a charge of appr. 50%.
One detail: When shutting down, the screen goes black, then, after some more seconds, there is a short vibration. This went way faster yesterday, no idea if this means anything.
After a few hours, I turned the phone back on.
Directly after booting, it showed a capacity of 3%!
Additionally, all 4 entries in the quick access menu were gone! The latter happened for the 2nd time already, again directly after booting.
Are these issues related?
My battery is one with the 14% bug. But it does not look bloated in any way.
I did not try the battery reset suggested above. Will try that next.