Confirming that update KB4519979 was the culprit. I uninstalled it and restarted the server, and now all clients can see the DVR (and all recordings were taking place in the interim, so I've got all of those as well!) Hopefully November's cumulative update will remedy this, or you guys get your MSDN setup squared away to assist with this troubleshooting. Thanks for looking into it!
Help and support for HDHomeRun DVR and HDHomeRun software for Windows 10, Mac, Android, XBox, etc.