In the latest build 4705 (2fedbe5) on High Sierra, the view cropped image option (P) crops the image as before, but moves it to the left of the screen instead of placing it centrally in the viewing area.
If the thumbnails are along the left-hand edge, the left-hand edge of the cropped image buts onto the thumbnails leaving a large margin to the right.
it was working fine yesterday, before upgrading to the new release.
Cheers,
Graham