Originally reported on Reddit here:
Vanilla doors of any kind will disappear, or the top half will disappear, upon exiting and reloading (single player) or logging out and back in (multiplayer, dedicated server).
This is a forge issue. I removed all mods and kept only forge in, started a single player creative superflat world, and placed each of the vanilla doors. Upon leaving and re-entering the world, either all of the doors are gone or only half of the door remains (bottom half)
Tested and confirmed on forge versions 2028 and 2041
This is not a chunkloading issue, I forced the chunks to stay loaded and the issue persisted
Occurs on single player or with a dedicated multiplayer server
