It looks like a few other people in the thread are having a similar issue:
I have a decent little shelter going with 29 people in it and 11 rooms. I bought a $10 pack of lunchboxed and found some pretty sweet stuff including Eulogy Jones and some legendary outfits.
I just openned 1 more lunchbox from a quest and got another lengendary person in it and sent him and Eulogy out into the wasteland.
I left Eulogy out and recalled this new guy and then went to sleep. When I awoke, Eulogy was still doing his thing, murdering everything in the wasteland, but the new guy didn't show up on my vault dweller list anymore and it showed 28 people.
When I click on Eulogy to see his log and loot, the UI shows 1/2 (meaning 2 people out in the wasteland) and lets me click over to the other guy that should have returned by now. His player model is a dead raider running and the button says "explore" meaning he should still be returning? I could click the button between explore/return and nothing would happen. It still showed the guys inventory and such.
So I closed the app and killed it by swiping it up. When I openned it back up it went through the motions and then i clicked "Enter Vault ###". The Please Stand By screen loads and the nuclear symbol in the middle rotates, and then it stops rotating and the entire app crashed back to my apple homescreen. I've restarted my iPad a few times and nothing helps.
Nothing I do gets me into my old vault - but I can make new vaults and they work just fine.
I am on an iPad Air 2 64GB - IOS 8.3 with 5 other apps installed (I just got it 3 days ago). Fallout Shelter works great on it and I've had a blast until this morning when this freeze issue happened.
Should I try to get a refund from Apple for the lunchboxes or wait for a patch?