Performed a Rebuild and now Photostructure has lost knowledge of the bulk of my pictures

Unfortunately, libraries are backward compatible but not forward compatible: Tried an alpha or beta build, and want to return to the stable version?

You can use :stable and re-create your library, or “upgrade” to :alpha (which works well on my hardware, but there are users that have seen issues with the latest :alpha, so no guarantees). Here’s my general guidance for alpha, beta, and stable: Alpha, beta, stable, and latest; What should you use?