Same here, it basically goes along the lines of:
If there are three human players (PCs), and one AI companion: First person speaks and we hear the voice, second person speaks and we also hear the dialogue, third person selects his line but the game skips it and voices the AI dialogue.
It's the same thing for two PCs as well, whoever is going to speak last before the AI gets skipped over and it really feels bad, like your existence in the game is just removed. Sure you're there, and it shows your dialogue as being selected, but it just feels really bad for those who want to feel involved in the story.
This is also with or without mods on two completely different games.
