Still learning I guess - and I can't re-create the actual sequence, but I did get it to work.

What seemed to happen is after I have it set to Violin as the solo instrument (exactly as your picture shows) it still says guitar in the track mixer.

But when I play the section where the solo comes it, it changes to violin and now has stayed there.

I know that sounds suspect - and so maybe I have it wrong. All I do know is it's right now.

Thanks much for the responses!