I think it's just a visual bug. He did recieve a rewad the game just didnt give the usual information box, that's why as you said, it counted towards the weekly mission. I myself have experienced this bug a few times already (I did recieve the rewards too) and what I usually do when any sort of bug occurrs is refresh the game. That "should" fix it.

I might be wrong, won't know for sure untill a mod answers it.