Comment by GoblinSlayer

Interpreting the hard problem as an epistemological problem looks trivial. There's nothing extraordinary in ignorance. The way you describe it implies we have the hard problem of ultrasound too.

I think it's ontological problem: structural description ontologically misses unobservable ideal substance, so the challenge is to provide a principle that would make ideal substance unnecessary. If you don't think too much, ideal substance ontologically solves consciousness, and it's not obvious how mere structural description can live without it.