I have a late 2015 iMac Retina 5K running Catalina 10.15.5. For about the last year I have been using an album of my photos in Photo as the source for my screen saver images. They have always looked crisp and clear, but as of a couple of months ago they only look clear for a while, and then they start showing up blurry. How can I fix that? Nothing about the setup or the images themselves has changed.