This is a little late, but hopefully this reply will still be useful.
I have a similar issue, and I think this is the cause:
The program closes if you move to a scene that doesn't have PNGTuber+ running back to a scene that does. I dunno why it does that, but it's pretty consistent for me and might be the same problem y'all are having.
The only solution I have for it is to have PNGTuber+ running in every single scene. You can hide it behind something or off-screen if you don't actually want it visible in those scenes, but it has to be active (with an open eye icon) to keep it from crashing.