WS2811 - Only 9 LEDs on, help with debugging

What you can try now is attaching the remaining LEDs to the end of the first working 9 LEDs. Hopefully the entire chain will then light. If not, that would indicate a fault with chip 3 also, but I expect its probably ok.

Also don't forget that resistor and cap I mentioned. It might be working ok without them now, but for long life and stability, they are a good idea.

Also, you may notice that when the strip is set for every led to be bright white, the LEDs at the far end of the strip are not quite the same colour, with a pink or yellow tint. This is due to voltage drop in the strip itself. It can be cured by running another pair of power wires (good quality thick wire) from the psu to the far end of the strip.