Using the _on_AnimationPlayer_finished won't work because I'm using an AnimationTree to mange my state, not the raw AnimationPlayer. Also, I'm encountering this even if the function call is moved to slightly earlier in the animation. I have to move it all the way back to the half way mark to be confident it will be called. Also, I feel the function ought to be called even if it is the last frame.
Those warnings are mostly Godot complaining about parameters that are never used.