I might be misunderstanding your wording, but are you implying she has another romance scene already coded in the game right now, and that it's blocked for some unknown reason?
No no it definitely is not in the game itself currently, but the way the whole scene plays out and how the next morning plays out is clear indication there is missing content that is supposed to be there.
Because Minthara's actual romance starts only after ACT 2's finale.
She asks for permission to touch our mind so she can feel what we truly see her as, a lover. To which she responds; "...there will be no Gods or anyone else, tonight I am fully yours".And... nothing happens after that. The very next morning other romances auto-break up with you immediately without even wanting to talk about it, while Minthara has absolutely no romantic dialogues nor reactions to it.
This massive gap between that night and everything that follows from that point onward is clear indication that Minthara is supposed to have an actual fully developed romantic scene, behavior change and dialogue about it which is simply not there so she has no romance at all because she is missing this scene.
Not to mention that even companions do not react correctly, it is a night and day difference. If you lets say hook up with Lae'zel while also romancing Karlach, Karlach has two different fully-developed dialogues with choices ready to break up;
- First one happens only if you approach her before leaving camp after Lae'zel's sparring where she is really jealous and annoyed at you for playing with her heart.
- Second one happens only after you leave camp so she gets a dialogue bubble where she acts disappointed, but understanding about it.
In Minthara's case companions don't have anything like that. They literally just go; "Oh so I see you have a piece on the side, m'kay". And that's it, whichever romance you had is now permanently dead.
Ultimately Minthara's non-existing "romance" is a miserably glued together placeholder from bits of scraps just trying to make it barely passable.