World loading from 18w16a creates a clear world without anything that i built.

So i was building a MC map in 18w16a and wanted to update it to 18w19a when i loaded it in 18w19a the world was a clear superflat without anything i built. Luckily i backed up so then i tried to also load it in 18w19b but the same thing happened. Same thing happed when i loaded a world in 1.12.2. My inventory does NOT get cleared when i load up from any of the new snapshots.