I was playing in the promotion steps of the quest where you need to win 2/3 matches to earn the promotion. I had played 2 matches and went 1W/1L. After my second match ended (win), the quest failed and made me go talk to shaxx and restart the 2/3 wins step.
I didn't even get to play the 3rd game before the quest failed.
To follow up on this. I played my third game this morning and won. I got the triumph for the division promotion and for achieving platinum in comp which finished my glorious title.
So the bug seems to be related to how the quest displays after 1W/1L and having to go back and talk to Shaxx. being prompted to restart the 2/3 grind.