Make nandroid backup first
1.flash custom recovery Twrp 3.0 recovery twrp-3.0.0-0-nobleltezt-nobleltezt.img.tar and flash using Odin.
2.reboot to recovery
TEST DEEP SLEEP
You can test with some CPU monitoring app too but this test simply test that above fix is worked or not. In spite of this application showing fixed and you are not getting deep sleep, Issue is somewhere else (may be app ot other and you need wipe)
How different this test app from CPU monitoring app?
This app simply test whether above procedure worked or not. It doesn't related to really your device goes to deep sleep or not. While CPU monitor confirms your device is having deep sleep.
After this Fix Install attached Deep Sleep Test 1.0.apk
Click on Installed App icon
It will give toast notification about fix status.(It is fixed or not)
Here is How to root N920C Marshmallow (UPDATE 4)
Thanks to @dadimon29 for test and correct order to flash
@combat44 for finding -Flashing xposed fix root.