As the title says, when I reunite the Roman Empire, it uses the same Imperial Elective succession type, except the option to nominate heir is just gone. And by gone, I mean that the button is not there. And neither do electors appear.

Some additional information:
- prior to unification, WRE had Agnatic-Cognatic gender law, ERE was still Cognatic;
- in the succession type screen, two more Kingdom titles appear, one has Agnatic Primogeniture, another one has Agnatic Imperial Elective. Both were handed out as Viceroyalties though, so they shouldn't have appeared in the first place. And for the second kingdom title Imperial Elective doesn't work either - the button to nominate heir is missing;
- i unified the Empire through double abdication if that has any relevance to this discussion;

Since I play in Ironman (don't ask why) I'm afraid of just saving and reloading, since it would derail further gameplay. Does anybody know what could be the cause?