There's stuff missing in the GUI, but only for my son and my wife :(

Are you on single player, LAN, or a server?

I'm on singleplayer, although I've opened the world in LAN a few times.

That happened to me on my private server, i disconnected and reconnected and it was fixed.

It goes fine when I do that, but it reappears after I get into the world several times.

Going to take a look at this later today.

Unable to reproduce this on my end using several different methods. Assuming that some previous fix may have already resolved this. If it happens again when MCA is brought out of beta, let me know.