A big thanks to chasfain and howardgilbert!
I was just looking back through this thread and had a little time this morning, so went through the thread chasfain linked and was able to get the DVR setup and working in sub 10 minutes.
Simply have the Plex Web Page/Client up and logged in, reboot the Plex Service (Or in my case the Docker), and as soon as it comes back up go to Settings > DVR and click Delete DVR (I rebooted the docker once more afterwards just to be sure, although it probably didn’t need to be done). Then re-setup and good to go 
