So, it's not a bug, Bioware really just thought locking out one of the most antecipated romance choices (by women and gay men especially, don't think we don't see you) with no explanation in game as to why that is the case only for him, therefore necessarily tying his romance to a harder time getting the best ending, was a good and interesting choice. And then, for some reason, they decided he should have better chemistry with Neve and romance her regardless of having "no time" for a relationship with Rook (SD Rooks especially were in the exact same situation as Neve and made the same choice). We were supposed to be able to romance any companion regardless of gender or background, as they said, but apparently you can only romance Lucanis as a SD if you compromise your roleplaying for the romance. And the reward is not all that, from what I hear. I've been seeing romance videos pop up and they're remarkably short for a game they said was so focused on characters and romance.
I would have preferred clear hard locks for romances like in previous games, based on the character's sexuality and background, because then at least I'd know straight away and understand. I wanted to romance Lucanis as SD, because they said any background was possible, but only possible if I'm willing to roleplay sacrificing my whole city, which is the better strategic choice, for the pretty boy, apparently. Meanwhile, Nevemancers get to make their choice and have a whole different dynamic/romantic relationship with her if they choose one or the other, which we should have gotten for Lucanis as well. It's like they didn't want us to romance him at all, like his whole romance was an afterthought despite him being so popular since Tevinter Nights. It's baffling to me.