Hi! Sorry for the trouble.
The problem is that the design that I chose to implement in 5.5 with an “auto-spawned” camera system actor as the view target was actually a bad idea. So I’m reverting that and slowly fixing the issues it created. Long story short: GameplayCameraComponents are now just running their own logic like any other camera component, and are recognized by the engine as camera components. And so, because I see you also have a FollowCamera component inside your actor, the engine now considers that you have two cameras in there. By default, this means it will just grab the first one it finds that is active. I’ll bet that it currently finds the FollowCamera first.
So you could try to first disable the FollowCamera (e.g. uncheck the “auto-activate”) and see if that fixes it?
I have a bit more information about the breaking changes in 5.6 on my blog. Since the plugin is currently still in “Experimental” phase, there’s not really any proper documentation for it. The Quickstart was sort of an exception.