ESPixelStick setup problem

[pobber]

I've tried searching on this topic, but I'm not quite sure how to characterize it, and not sure where in the chain my problem is.

I've used XLights to create a simple 500 pixel test sequence.  I have a single Null controller defined in Xlights, set to Auto Size.  I have saved this sequence to FPP library.

I have one output in FPP, a multicast to one ESPixelStick, Channel and Universe starting at 1, Universe Count 4, Universe Size 512.

ESPixelStick is functioning well, and addresses all 500 pixels in the circuit when using its built-in effects.

When I play the XLights sequence through FPP, only approximately 350ish pixels are lighting.  The last pixel lights only the red channel - I'm sure this is meaningful, but I'm at a loss.

Can you help with any settings to check or troubleshooting steps?