It seems like GOG is a really big pain to give updates to, because this is the second game that has had a major free update on Steam, but that isn't on GOG. The Dev has stated that they plan to update the GOG version in the future, but it seems like GOG is just giving them a hard time for some reason. Buy on Steam until the situation is resolved. This 100% is not the dev's fault so please don't give them a hard time about it.