I, too, am missing iStock. I did as suggested and redid the moving block puzzle and uploaded the files (twice). Reloaded my loot page. Still no iStock in my loot.
I'd like to point out that I never got a second (new) briefing in the middle of the mission. It gave me the same briefing from the beginning of the mission. Perhaps that is where the screw-up is.
And if it matters, somewhere along the way I got a page here that said I had completed the mission.