I'm currently doing an Origin Astarion playthough, and I romanced Shadowheart this time. I *did* trigger the Act 3 romance scene for Shart, even with Patch 4.
* I made her Selunite Shadowheart, so she has silver hair
* I interacted with the NPC near the refugee camps in Rivington
* I took her to Sharess Caress, but did not speak to the Drow Twins
* Did not do the romance quiz at the circus
* My approval rating is at Exceptional with her.
My main question for you is, did you rent a room at the Elfsong Tavern?
I triggered the Shadowheart Act 3 romance scene, while camping outside, literally the first night we were in Baldur's Gate lower city. Normally I talk Alan into giving me a free room at the Elfsong, but this time I had all my characters sleep outside by the docks. Right before the romance scene, she had an exclamation mark above her head, and she talks about how she needs the water to cleanse herself and tells you to meet her that night.
The same night, I got the romance cutscene (skinnydipping), and the next morning she jokes about how she's still finding sand in her hair.
If you want to try the route I went, try and find a save before you rented a room at the Elfsong. Do a longrest while camping outside in lower city and see if you can trigger the Act 3 scene.
