I just finished a rank SR game and got S- as karma, but I didn't get my mastery token. I'm rank 5 mastery right now, so I should theoretically have gotten it. Is it a 100% drop or is there some limitation I may not be aware of?
The only limitations that I"m aware of is like the fun modes and aram don't hand out mastery 6 tokens I think
Did you reached lvl 5 with Karma 
the same match as you earned the S-?
Because that the S- not yet counts
MikoSlam
Sometimes the notification will appear late/not at all. I'd recommend checking your loot, you may have it already without knowing.
