Wrong timings for controlling APA106 LED's using the neopixel Library

That's an odd one, I'm surprised this came up. Although I seem to recall I may have experienced the odd flicker even with WS2811 - it could possibly be an interrupt thing.

One thing you could try - before the neopixel library, the code we used for sending looked like:

SPI1.setup({baud:3200000, mosi:B5});
var arr = new Uint8Array(57*3);
var pos = 0;

function getPattern() {
  pos+=0.04;
  var c;
  for (var i=0;i<arr.length;i+=3) {
    c = 10+Math.sin((i+pos)*0.1324)+Math.sin((i+pos)*0.1)+Math.sin(pos)*0.2;
    c = E.HSBtoRGB(c-(0|c),1,1);
    arr[i  ] = c;
    arr[i+1] = c>>8;
    arr[i+2] = c>>17; // blue too bright
  }
}

function onTimer() {
  getPattern();
  SPI1.send4bit(arr, 0b0001, 0b0011); 
}

setInterval(onTimer, 50);

So I guess you could try SPI1.send4bit(arr, 0b0001, 0b0111); which should add 50% to the time for a '1' - and see if that helps