Further confusion. My board works with the other Pi which is still running the old/original python code. I pulled a capture using the Saleae and the output looks “cleaner” and another thing is the OE pin is toggled while writing. That’s something the new unified code doesn’t do, so I’m wondering if something there affects timing or sensitivity on the shift register. I’m fine talking to myself as I go through various things to test, but anybody with additional debugging ideas, feel free to chime in! 😉