OK I tested logging in to Xbox live from Safari on the ipad, that works fine. Then tried to launch minecraft and just see a solid white screen. Doesn't seem to be that Xbox connectivity is the problem.
Thanks, we had actually tried removing and reinstalling the app before posting.
He has it working now by disconnecting / reconnecting wifi multiple times every time he starts and saves his game. He says it's fine, he's just so happy he can play after facing the white screen for who knows how long; he insisted it was loading while the white screen was up, but I'm pretty sure the app was just crashed or permanently stuck.
I was able to create a new Xbox live account and login from my PC, so it's not a network-wide issue; I'll test xbox live from the ipad when he's done playing. Thanks for your help.
Here's how the Settings > profiles looks, once we turn on wifi the app crashes and can't restart. thanks for any help,
thanks Jonathan, I had tried that but doesn't seem to be signed in to Xbox currently. The Settings > Profile offers a button to sign in to Xbox. I tried signing into it or creating an account, but it has the same issue; when wifi is connected it won't do anything and without wifi it doesn't bring up a login prompt.
SAME PROBLEM, LATEST IPAD, NO XB FOLLOWERS
This may be a duplicate of https://bugs.mojang.com/browse/MCPE-29021 however since that is marked 'Resolved' and this is most certainly NOT resolved, let's keep this ticket here or reopen that one or both. This is infuriating and we'll be seeking a refund for this game if it's not fixed henceforth.
From the white screen, we can pull up the settings overlay (aka 'control center') and shut off wifi, then the app loads without restarting.