Welcome to the Forum UU
Have you Mic'ed the two Slide Stops to compare them one to one ?
If they are the same, than your RAMI is at issue
The Cross Pin on the Stop "may be" bent
Even the tiniest amount could be causing this issue
Since you've stated that the Stops will not interchange, and if they do Mic as different, then I'd say the Stop is at issue and a new Stop would be your fix