I think there can be genuine feelings there, and especially if the T self-discloses a lot. But if it feels more obsessive or fixated than friendships do, I would still tend to think transference is mixed in.

I'm also not sure how one could tell if maybe the transference was long-term and unresolved because of ineffective therapy, as opposed to something else? That's not to cast aspersions on the T, just that sometimes one method or model works and another one doesn't. Transference could linger because the right approach hadn't been found yet with that T (or because a different therapeutic relationship was needed).