Alright - it's got me stumped!
What happens if you start a brand new project with NO plugins, and set up your actors and system tab in the same way (you'll just need those two actors, but put them in the same slots), and add the event where you change party members? Does it work then? If it does, it could point to a plugin as the issue.
Edit - oh, when you test play, are you choosing New Game each time? If not, do that, and see if it makes a difference.
What happens if you start a brand new project with NO plugins, and set up your actors and system tab in the same way (you'll just need those two actors, but put them in the same slots), and add the event where you change party members? Does it work then? If it does, it could point to a plugin as the issue.
Edit - oh, when you test play, are you choosing New Game each time? If not, do that, and see if it makes a difference.

