I experience the same problems with 30 tapes of 118 pixels. The problem occurs when more than one output is used (4x118px). have tried a lot of everything. including the level shifter. Sometimes the problem disappears when using a ferrite ring. I’m at a loss.
Was just thinking - another thing you can try is adding a null pixel in each of your data lines (or just the one that is flickering), might help clean up the signal. If nothing else, it might help you troubleshoot.
did you ever sort this out. curious and a chance for all of us to learn something.
I managed to overcome the problem in this way: https://youtu.be/letCT3vq8V4 If you do not use more diodes than the power supply, then everything is fine.
In his circuit eliminated the capacitor