Fallout – The Party at the End of the World #6 quest reward

The quality of items you find is directly tied to the length of time the dweller is out in the wasteland. Their survivability of course is related to their level (health) and the number of stims/radaways you give them.

Basically just wait longer. The longer they are out there, the better chance of getting a better drop. There are no guarantees of course, but if they can survive out there for several more days, leave them for as long as you can and you should get better drops. Since they take no damage or radiation while on their way back, you can wait until they are literally 1 hp away from death before recalling them to get maximum exploration time.

I have had this happen twice, and it annoyed me.

Simply closing the app, flushing it from memory (double tapping home and then swiping it up to get rid of it) and restarting it cleared this up for me. They (cause it was two for me) loaded back in just fine with everyone else.

If that does not work you can try sending em to the wasteland for just even 30s (enough to get em off the screen) then call em back.

They just need to be reset is all.