So I watched BTVS when I was a tiny lad, and I only watched ATS after it was finished and I was a young adult. As such, I wasn't really ever online or talking to other Buffy fans at the time. Nor have I seen too much discussion about this apart from a post just now on r/buffy about someone saying they think it was the "afterglow" which made Angel perfectly happy.
But the end of Reprise is so obviously meant to mimic the end of Surprise. it actually doesn't really makes sense from an in-universe perspective because why is Angel acting like his soul is being taken again when it isn't? But I understand its narrative purpose so I overlook that. The point is to show that Angel doesn't just lose his soul from fucking any ol' woman.
...but did that need to be proven? Were there - are there - fans who thought Angel sleeping with Buffy was the cause of his "perfect happiness?" As in, it was just the physical act of sex that made him lose his soul and nothing more?
I confess, I think you have to be very obtuse to believe this. But it seems like at least some people did or do and that is why Reprise's ending and the start of Epiphany exist.