- Edited
Update:
Behavior repeatable in safe mode.
- Power on device -> Google -> Graphene -> Lock screen
- Press and hold power button until power options show on screen
- Hold down the power off option on screen
- confirm that you want to place the device in safe boot
- device boots in safe mode
- safe mode is shown on bottom lefthand corner of screen
- wrong pin shows "wrong pin" message
- correct pin gives black screen and or "System UI has stopped working"
Accepts CORRECT pin, and splashes black screen or "System UI has stooped working" once again locking