I was able to get 100 points and trigger the best of 3 series.
I won the first one yesterday. I played a normal today to warm up before attempting ranked (won it), then played a ranked game (2nd game of the series). We were able to win that game as well, but afterward, I received a message saying that I have just triggered the best of 3 series again.
Going to my league page, it shows three blanks now (effectively ignoring my two wins) and I haven't been promoted as I should have. I tried logging back in with no luck.
I have yet to attempt a 3rd ranked game (which would be the last of the series) since triggering the initial series notification. Do I need to play one? Seems silly since it would be unnecessary for me to move on. Regardless, the loss of record for those two series wins is disconcerting.
Update: I played another ranked game and won. It's showing that I have won my first game of the series when in actuality, I just swept it.
I looked at my match history and the order of events basically goes like this:
Won at least 3 (cannot see back further than that) solo ranked games consecutively to get to 100 points
Receive the initial best of 3 series notification
Play a few normals with friends (didn't want to play ranked due to division differences).
Played a few ranked 3v3's with friends. We lost them, but since it has it's own ranking, I don't see why this would be an issue
Won solo ranked game as 1st game of series
Won normal game
Won solo ranked game as 2nd game of the series. In post game, I get the best of 3 series notification again. The record of my 2 wins is wiped from the League page but still in my match history
Won ranked game with a friend of the same tier. This would have been my 3rd of the series, but instead it is showing as the first of the new series.