I have no clue what happened, but after unlocking final lore challenge of Phoebe, I also received rank 15 rewards : skin and “Master of Phoebe” title.
Here is a screenshot, in it you can see that “Complete a match at Character Rank 15” is not done, but I still got the reward.
Screenshot : http://steamcommunity.com/sharedfiles/filedetails/?id=680487654
This bug is very minor, but still it would have been nice if it was fixed.
