When working with scrollable areas in your prototype, you can't use pinned comments, because they ignore the scroll position of the area. So it's not clear where the pinned comment was intended to be.

What I would expect:

Pinned comments can be placed in a scrollable area and when they do, they scroll along with the area (and can be outside the viewport)

This way, I can easily collect feedback on the content inside a scrollable area.