Slurs attach to notes. If you position an end visually without making sure it attached to a notehead, then it will be unreliable when automatic spacing alters in different parts. Of course a slur will connect the same noteheads in the score and parts.

If you are talking about the arc of the slur, adjusting it in one part should not change in the score.

Thanks for the help.  I think attaching it to a note may be my issue. - Bruce J