I can tell you that the Allen Bradley drives I use say to connect the encoders shield at both ends and I have done that on some and not on others and never noticed a difference but I am talking normal incremental 5v square wave differential encoders.
I also have some motors with sick stegman sine/cosine encoders and they will just not work without a shield or the shield only connected one end, they need the shield connected at both ends.
Now I have seen all sorts of explanations of how to shield and where to connect and some of the explanations have mentioned that it is frequency dependant. I have always tended to connect one end only as that seemed to be current thinking but like everything else, thinking changes and you can never get a clear answer.
I say connect one end and if you have problems try connecting both, if you still have issues then start crying (would pull my hair out but its already gone
)
Hood