Had the same problem. Installed the first edition just after it came out and played it for a few hours. Had chance to have a full night on it as the wife went on a holiday with the girls. Sat down loaded it up and thought why not buy some lunch boxes. (cheeper than a night out with he lads) 40 bought and was just starting to use the first 3 and got a couple of good dwellers from them. This took my dweller count over 20 and it crashed. Could not get back in no matter what I tried. Left it for a week and I got my confirmation email from the App store for the 40 lunch box purchase. It said bla bla bla but also said if you have a problem with this purchase to click here. I did this and it went to the app store help page, where I filled in my concerns as to a purchase made and not being able to use the bought items as the App no longer works. I also mentioned that this was not an isolated case and the fault was wide spread and searchable on the internet. I got an email back with in 24 hrs to say that they were giving me a full refund and if there was any thing more they could do, not to hesitate to contact them.
This is what should be done to make sure that a fix it put in place to rectify the crashing problem. If everyone who has bought lunch boxes goes back to Apple and claims for items not fit for purpose, the fix will come.
After the the update on the 10th I tried it again and bingo the vault worked again. I worked with it for a day. Was working OK ish unto last night when it was crashing every 20 mins or so (but was living with that) This morning no go. Cant load in, just after the "enter vault XXX" crashes back to home screen. I still get the messages saying one of your kids has grown up and you have a new baby. I was at 40 dwellers and over night it hatched a new dweller so it looks like my new limit before crash it 40. 41 is a no go.