Pls install latest bootloader via fastboot.
Pls unzip the Update.Zip package and install boot.img via fastboot.
Pls install TWRP 3.1.0-2 via fastboot
Reboot into recovery via hardware keys - not into system in between.
Restore your last backup.
You may install supersu at this point.
Reboot into system
Thanks for the quick reply. I'll try that and let you know.