Double-click on part 2 in the composer to open that in the performer (which is already open with part 1)
The focus of the performer does not move to the new part. My "workaround" is simply shutting down the performer and re-opening part 2 to make that focused.
Steps to reproduce:
The focus of the performer does not move to the new part. My "workaround" is simply shutting down the performer and re-opening part 2 to make that focused.