So I know some other people mentioned this but some of my champion skins are not unlocking. I played one match with each of these characters and they didn’t unlock.
Gligar35
(Gligar35)
#2
Hmm, same thing happening to me. I am slowly getting them for some reason. Hopefully they can fix this.
Play matches with at least each faction. also do the first and third PVE missions. and a PVP match. i unlocked all of them by playing a few matches in each mode and the prologue as well.
I actually figured it out. You kind of have to retrigger the challenge. For the ones that are map related, you have to play a mission on that map, you don’t have to win, just go in. For the ones faction related, same thing, just play that character. I have them all unlocked now. A bit annoying but only took about 5-10 minutes to kill myself on the four story missions i needed to.
DevilJoe
(DevilJoe)
#5
I just played a round of Draft Mode (Meltdown) and collected Kills and Assists.
Phoebe and Reyna’s Champion Skin do not unlock anyway 
For the rest of the already completed challanges it does work when replaying the mission or faction.
That’s odd. First thing I did was kill myself on the algorithm and those two were in my rewards. I’m sure they will unlock eventually
DevilJoe
(DevilJoe)
#7
Strange, now i have them but can’t remember if i got them after a mission.
Fine enough ^^
Gligar35
(Gligar35)
#8
To get starting 7 characters champion skin, you need to do the prologue. Just got the cool orendi skin out of it.