So, technicalities first: my phone is a plain old Moto G running on Android 5.0.2, or "Lollipop".
The issue occured just seconds before a particular dweller of mine was to return from a 1h30 trip to the wasteland. There was nothing else happening at the time that could be considered particularly interesting. A baby might have been born or something, but really it was business as usual.
The dweller that was about to return had good stats, probably a rare dweller, and he was wielding an equally rare plasma pistol. He was wearing a sports fan outfit, or similar low-level jacket. That being said, this dweller of mine had been out of the vault before and in similar gear, so the problem is not likely about him. Rather, I think it is something he was carrying.
I remember the dweller was carrying a dark, blocky, conventional pistol in his inventory, some caps, stimpacks, and nothing else. The gun might be a 10mm perhaps. It didn't have particularly great stats, but the import any bit is that it was unlike any other gun in the vault.
Now, since my game crashed the moment this new gun came anywhere near my vault, I think the item must be glitched, corrupted, or whatever you want to call it. That's just my speculation, though.
Anyway, it would be great to be able to play this game again. However, right now it seems I have to start over, because this game is totally jammed.