Level 47 dweller disappeared while exploring the wasteland

This may have some causes. Please check the following things:

1. Is he really lost? He is not in the wastelands? He isn't dead in the wastelands? He is not in your vault and not in front of the vault door? Did you check your dweller list?
2. He wasn't dead in the wastelands for more than 24 hours as they should not be able to be revived (at least in the vault) after that
3. He may look different if he find better equipment (weapons/outfits) as he automatically equip those better equipment.
4. You may close the game, remove it from the background running tasks, lock your phone and unlock it (to start the garbage collection). Restart the game. Is he still lost?

Hopefully this will help you, finding the possible error.