Random flashing on WS2812B LEDs
The data line in a string of WS2812B chips is not a shared bus as it might appear. Instead, each WS2812B retransmits each bit it receives down the line at full Vcc voltage so there really is not any "fade" with respect to voltage as you go down a string. If the first pixels is seeing enough voltage to see the bit, then all the other pixels downstream should see it too.

First, I'd make sure you have enough power injected along the length of the string. You can test for this by driving the string dimly with less than, say, 20 brightness for all three colors. If it works fine with the dim colors, then you almost certainly do not have enough power getting to the end of the string because of the voltage drop on the power lines (not data lines). Those flexible PCB strings have relatively high resistance, and WS2812B chips can use up to 0.25 watt each, so the voltage drop along a string of pixels can be high enough that the pixels at the end do not have enough power when the current demands (and therefore the voltage drop on the power lines) go up. Easiest way to fix this is to add wires going from the strip back to the power supply every 2 meters or so. 

If you still get flakeyness at the end of the string even using dim colors, then the next place I would look is at the timing of the signal coming out of the Beagle-Bone. You might possibly not have enough room between your bits as described here...

http://wp.josh.com/2014/05/16/why-you-should-give-your-neopixel-bits-room-to-breathe/

One way to test for this is to connect the string to an Arduino and use some time-tested code to try driving it. If this works, then I'd look at your signal timing on the BeagleBone and try adding maybe 100ns of low after each bit. 

Report back with what you find!