Another thing you and anyone else having the issue could try is going to placeable_instance.gd and editing the save function from
```func save(p_include_uid : bool) -> Dictionary:```
to
func save(p_include_uid : bool = false) -> Dictionary:
So it has a default value temporarily. This seems to be a demo specific bug but shouldn't effect regular plugin use. I will be sure this is patched for the next release which is soon.