I am testing PhotoStructure (alpha6) on my Pixel 3 smartphone. PhotoStructure is currently rebuilding the library. The eader with the “Rebuilding your library …” message is too wide: This does not look nice and requires the user to scroll to the right to see the button for switching the thumbnail size.
Second observation: For pictures does not seem the be a good amount for this screen size. It should probably be at least six (to fill the space) and I’d argue that a bit more would be good to see a larger sample.