The level converter you linked is very likely not suitable for this kind of application. These transistor shifters tend to be too slow for NeoPixels, which leads to pulse-shape distortions, causing all kinds of problems. Unless your data line is longer than approx. 1 metre I suggest you try a direct connection with an inline (series) resistor of about ~50Ω. And if that does not work out, then try to get your hands on a 74HCT245 level shifter.