Cassette spacer question for mechanics

Shifting is fine on DA10 cassette with an easton wheel. I switch the cassette to a Mavic Open Pro and cannot get the shifting to be smooth. The easton had 2 small aluminum spacers installed at LBS. I have tried both, one and none and it is not not smooth. What am I jacking up? What is correct? Thanks.

JK

Often different wheels have slightly different offsets from the dropout to the cassette. You may need to tweak the cable tension a bit.

Should I use 1 or no silver aluminum spacers?

I think you need to use 1 spacer. Whatever allows the lockring to properly engage.