I am running Hyperbian and have RPi3 wth WS2812 LEDs and a logic level shifter. I had pretty bad flickering. I did have everything on the same ground, i.e.: the LED strip, level shifter, and RPi were all grounded together but I still had flickering.
I decided to try adding multiple grounds from the RPi to the common ground plane and it stopped my flickering!
I have 3 grounds from the RPi to the ground plane. RPI pins 14, 34, and 39 all go to the LED strip ground as well as the level shifter ground.
I hope this helps someone else with flickering issues!
Now if I could get rid of the 0.7 sec delay...
-Vin