This is an issue in prototyping:
Even if the ‘Reset Scroll Position’ box is unchecked (i.e., not selected), the prototype will still reset the scroll position unless all the frames involved have a ‘/’ (Forward Slash) in their Title.
The position of this ‘/’ can be anywhere in the Frame Title, but without it it the prototype does not adhere to the scroll position retention.
IMO, this is a Bug rather than an intended use case and should be fixed.