The channels shown in the guide don’t come from the left-hand list of “Device Channels,” but from the right-hand list of “Guide Channels.” So, ensure you haven’t selected any of the 10.x guide channels in the list on the right. Perhaps Plex automatically mapped them to the wrong device channels?
Nope. None of the Guide Channels on the Right are the 10.x channels.
As an FYI, I did have to fairly recently go through the process of deleting the DVR and creating a new one and re-scanning for channels. Is it possible this is somehow left over from the old DVR?