For the ones stuck at %100 without achievement popping up, try opening the Quantum Break on Achievements application on Xbox One. The achievement will pop up immediately.
--- Update 2018 ---
By the look at the reports, this solution does not work anymore as of 2018. I didn't try this personally but according to psybOltOn, you can play Junction 4 by choosing the other option that you haven't selected the last time. This will reset your collectables for the last act. Replaying through Act 5 Part 1 to recollect the three computers shall give you the achievement.