Is there any way for the Evangelical Union Event to not fire even when there is a Protestant Elector?

I've been playing an eu4 game in ironman mode as Brandenburg. I've become Protestant in order to form Prussia, however, I also have toyed with the possibility of becoming Emperor. In order for me to do this, of course, I need the Protestant side to win/tie the league war. But despite the fact that both I and the Palatinate are Protestant Electors, the league interface has not appeared on the HRE screen. That is where it appears, right? Is there any way this could have happened, or is eu4 just being buggy?

Edit: Oh, and I should add that the Palatinate has been an elector for over 20 years now.