I encountered a weird problem today that I've never seen before. I imported some photos from my iPhone to Photos on my Mac mini. When I did that, all images system-wide went haywire though my desktop picture was fine. I could see the thumbnails of the images I imported into Photos. But if I double-clicked any of them, Photos would give me a blank screen. If I opened any other image from my mini or from an external drive, the preview window would be blank. If I opened an image using Affinity Photo, it would open a properly sized canvas containing nothing but a transparency. I tried doing screen grabs of some of the images, but those screen grabs also opened up blank. I tried emailing images to myself. Those also were blank. I tried altering some images in Photos, and when I did the thumbnail went permanently black. It was really strange. I restarted the mini a few times, but that didn't do any good. I called Apple tech support. They had me boot into safe mode and restart, and that seemed to fix the issue -- except for the images I altered in Photos; those still had black thumbnails even though I could open them up. They gave me instructions on how to reset my Photos library after I make a backup copy of it (which is going to take a loooong time). We'll see how that goes. I'm not too concerned about the few black thumbnails. I'm just glad I can work with my images again. Has anyone else ever encountered something similar?