All Pop-off weeks completed no reward.
All challenges completed for all 3 weeks of the pop-off event and week 3 was bugged after completing 16/12 was reset to 0/12. The challenges were then completed again with one challenge missing at 11...
Ideas
Completing all the challenges was not the only thing you had to do to unlock the vest, you also had to purchase the vest from the shop for 1250 event currency, a relog might've been needed once they were all done
There's been a hidden item available for completing all challenges in all events so far so keep an eye out during the next one