Hi there!
I think it is always best if you could ask them to take a look into this. For two reasons:
1 - Their plugin is paid and mine is free
2 - Their plugin is obfuscated and mine is not.
Now, a console log with the error trace could also be nice so I can take a look and see.
Probably they created another game object character, like a game event, to handle furnitures. And somehow something is different. Or even, a new Sprite_Character that does not have a character. Then it's null, therefore, it cannot have the getExtraProps.
You can try to open my plugin, and on every occurence of the character on the Sprite_Character code, you can do that:
Still not guarantee that everything will work properly. Just a wild guess based that I don't have neither the plugin neither the console error trace