Yesterday I noticed thumbnails were missing in my library for about half the shows. Ones that were there the day before. I use Apple TV to watch and the DVR is on a synology NAS. I opened the channels app on my iPhone and there were no thumbnails at all.
Is your dvr server able to talk to the internet? Check the Support > Troubleshooting page on the dvr web UI
Apparently it was not. Fixed by rebooting the NAS. Thanks again for your help