I did one PT recruiting Minthara, using the "evil" path. Recruited her before patch 5 came out, but ended the game with patch 5.

What I find incomprehensible is that after the end, there was a nice intimate scene with Minthara (no sex, just talking), complimenting eachother, declaring love and making future plans. You can chose different futures for your couple.
Some months later, at Wither's party, the dialogues change depending on the future you chose. You talk about the progress you made in this or that direction.

So this seems to be all fine and well worked out, but before the end of the game, there is no hint about any progress or development in your relationship with Minthara. When she calls you "my love" right after you end the main story, it comes as a surprise really. " Oh, so we were, actually , a couple ? Surprise. Since when ?"

That is why I find it hard to believe that the actual content of the "building up to a couple" is missing from the game. Why put all the effort in the post-story wrapup and nothing in the actual story ?
So I guess there's a bug that blocks the in-story progress. But how can Larian have missed this ?

I guess they can't test the whole main story and side quests in all variants for every patch, so probably they have some saves in certain conditions that they use to test. Then maybe fix some bugs, retest etc... until it works. But if the "saves" from which they start testing are not updated from the beginning, they may initiate from a situation that cannot be reached anymore because of other changes earlier on.

Not trying to find excuses for Larian, but I just try to rationalize why the post-ending is there and not the actual in-story scenes and dialogues.