from my understanding the fix just prevents you having a forced sex scene if you said no or yes and the bit I quoted that what I assumed you encountered. At least I recall reading previous complaints about that in the past. tho I don't even remember her being FWB I wonder if that is a new change or something I forgot as I haven't played the rework parts yet. Last I played I recall just having 1 conversation with her and an option to ask her out or not. I think someone even tries to push the MC to ask her out too.
You're probably remembering this convo:
Mom "I heard you and Cynthia have been "hanging out"."
MC "Did she tell you that?"
Mom "She seems to like you."
MC "She's good."
MC "But she doesn't want anything else, if that's what you're thinking, except to have some fun."
Mom "Spare me the details now, will you?"
MC "Haha!"
MC "She doesn't want anything serious, that's what I mean."
Mom "Sure, sure..."
Mom "She is right, she's too young for any kind of entanglement."
It's good to know there's an actual bug involving her, though. I'll hold off on doing new per-LI playthroughs until the update drops.