Hey, 

I was stumped by some odd render results and found that if Arnold motion blur is enabled and 'Keys' is set to an odd number the fur renders incorrectly, but on even numbers it renders fine.

I was able to replicate it on a furball in:
maya 2019
ornatrix 3.2.3.27923
MtoA 4.2.3

motion blur details:
Enabled True
Instantaneous Shutter False (though the issue also occurs with it on)
Deformation True
Camera True
Shaders False
Keys 3 (or any odd number)
Position Center on Frame
Length 0.5