the item-number shows "0" when I edit the world in different versions (I create in 15w14a, reload in 1.20.4 and finally loaded in 15w14a again)

 when I edited that world in 1.20.4 (1.20.5 exactly, but not important), it looks like I'm stuck in somewhere, and more weirdly, I have actually nothing but in my bag there, things which numbers "0" were shown.