Found this one a couple of hours ago in CS. It turned out it's a known bug that's been occurring for the past 2 weeks but, obviously, was unknown to me until today.
So, I got 2 reward boxes for the same match. Luckily, we won, otherwise I wouldn't have noticed it.
I doubt it matters that it was my first match for the evening but who knows. Match ended at 21:38 CEST.
It seems it's an individual bug, not affecting the whole raid. It's possible I've got it in the past 2 weeks again without even realising but I usually keep track of how many wins and boxes I get for the night.
