So I started a game and after some turns, I made a break, saved and quit the game. Once I came back on the game the leaders I choose to face were changed into someone else.

So that's it I choose some leaders at the beginning, saved and quit and "aliens" (for my personal role play) replaced them.

@grifenpierre It can either be that You first booted up being online and connected to Your Games2Gether account to access the special creator avatar AI's, which are linked to Your Games2Gether acct. If next time You boot up You are either in "offline mode", or not linked to Your Games2Gether account, those AI's will be replaced with regular AI's and portraits. Even if You load a save file from previous session when You were connected.

There also seem to be a bug where both difficulty settings will not take effect and are set to what was saved from last session. 

As well as a bug where some AI's will be replaced in-game in next session. Not staying the same as in first session. Even if loading a save from first session. @GamerZakh had that happen in his stream and ended up having one AI being him, so he played against himself.