I was testing out the soul form mechanic on another world, went through one zombie, two skeletons and exited the world as a soul. I loaded up my actual world and my item hotbar is gone! Not the xp, health, or hunger bars; or my inventory for that matter. Just my item bar. I tried changing the GUI scale, gamemodes, and my resource packs. No change.

BUT, for future reference fellow players: a quick restart of the game fixes it. Just exit and use the launcher.