Did you happen to open your vault with the device time set incorrectly? I'd be tempted to set the device time forward 2 years and open the vault, but that might trash all your calendar reminders and such.
Can someone please help i let my little brother play on my phone and he messed with the set time on my phone (he skiped four days ahead, i set the time back to normal now) but every time i send out a dweller into the wasteland no matter how long they still dont bring and items back.