Ran into this issue many many times. To fix, stop all plex services and go to \appdata\local\Plex Media Server\Plug-in Support\Databases and then delete tv.plex*.*
Then reboot. The DVR will be back but you’ll have to refresh the guide.
Hope this helps!
Update - After running into this issue yet again… This time I had to delete the DVR and re-add after deleting the files. Deleting the files brings back the DVR so you can at least see it to delete and re-add.
