I don't understand this kit worked perfectly fine for me during the test when i was using it on steam but since it officially released i had to reinstall it from GOG since thats where i purchased Witcher 3 and now i can't open an existing world i worked on for days and can't even create new worlds as a test, this kit is completely broken for me.

Same here, I tried several installation, then I deleted all the things. I'm waiting for an update.