I am also experiencing similar issues (including a black-blank screen). I have been using the Apple TV 4K (ATV) Home Sharing Screensaver feature for 2 years without issue. I don't stream photo’s; I stream my iTunes album art library (images). Recently on 3-10-20 I had added more album art into iTunes so I refreshed my Home Sharing settings (PC & ATV) to include the new images (had no issues). On 3-24-20 I updated the ATV firmware to 13.4 (17L256). At that time, I still didn't have any screensaver issues. It
wasn't until 4-19-20 I once again added more album art to iTunes and again refreshed Home Sharing did I then experience a glitch. My album art screen saver is set to display as tiles (28 individual album art images) on the screen. The noticeable glitch was now displaying some of the images 4 times each. After refreshing Home Sharing in hopes of fixing the glitch I then received a black-blank screen. It appears (in my case) everything Apple (screensavers) still works. All the album art created by iTunes (iTunes downloads) still works as a screensaver using Home Sharing, but all the album art I downloaded from
the internet and loaded into iTunes doesn’t work (now a black-blank screen) like your personal photo’s. One thing I did notice after changing the screensaver display options (in my case I switched from cascade to flipping the image) I could make out/see a shadow /or placeholder of the image on the black-blank screen. I have tried the usually troubleshoots, ATV restart, unplugging the ATV, and signing out and back into both accounts (PC & ATV). I have only had to reset the ATV back to factory defaults one time during the firmware update 13.0 disaster. It’s a major pain. If that becomes the case, make sure you jot down (take a pic) of your primary settings. I’m in hopes that a firmware update will fix this issue like it did the Sleep Timer fiasco. It did take 3 firmware updates after the fact to convince Apple they had an issue left behind from 13.0.