Thank you for your detailed feedback.
I agree that passing through a barrier should have a different sound than picking up souls. I had planned to do that change, but forgot about it. :P
About the barrier collisions, I used simplified box colliders on them, so maybe there are some corners sticking out a bit from the actual barrier mesh. I'll have to refine them or try changing them to mesh colliders and see if that doesn't impact the game performance too much.