imported pictures have older pictures as their preview picture
After importing photos from my iPhone 7+, Photos doesn't show the new pictures, but instead show a preview of an older picture in the library. This is totally random and not all pictures are replaced. By hovering on the picture, the preview is replaced with the intended imported picture. after moving the mouse, the older preview picture replaces the intended import picture.... metadata shows the new picture information....
iMac, macOS High Sierra (10.13.1), 10.13.2 beta (17C60c)