While playing in my survival world, some parts of my HUD dissapeared. Hearts, hunger and armor all vanished, but the XP was still visible. I have no idea of how to reproduce it, but I first discovered it while swimming up a soul sand elevator, but thats probably not how to do it. Most actions does nothing to fix it, it even persists through closing and reopening the world. I had to restart the app to get it working again.

Some video of it: https://youtu.be/7E4V1VEr5pM