Promotional series glitch (?)

Ranked has been pretty hell for me this season, so this was like my 3rd time making it to platinum3 promos. I played a Leona game which I won, which got me into promos. I then played a Janna game for my first win, and finally a Braum game which I lost. Now, since the Leona game was the win that got me to 100 LP, the next two games should put me at 1 -1 in a best of 3 for platinum 3, right?

Well, upon coming out of the Braum game, I find a message telling me that I've been unsuccessful in completing my promotional series.

Am I missing something here? I've played on and off since season 1, and am pretty sure I've never encountered this before.

[sg-janna]