my phone is LENOVO ZUK Z2PRO ZUK Z2121,MK71.2-z2pro-190128-release.
I have same device. Problem is happen on both device.
I take picture, and screenshots.
Time to time, these is failed.
File is not saved.
Strage space is over 15〜30%.
I don’t know reason.
This file saving error was happen often when open camera by shortcut and picture.
This shortcut is without finger print security.
It is by double touched power button.
So take picture at once by volume button after open camera.