I have an 830 and i record both NEW survivor (higher priority) and masked singer but i have them both set to record a specific channel to avoid the problem you are explaining. You are correct, because to experiment i changed survivor from a specific channel to record only HD, and then then the pvr is set to record survivor on both tuners, with conflicts on about 20+ other channels and it will not be able to record masked singer either. If i change survivor back to one channel, then the problem is corrected. I believe the problem is that survivor doesn't appear to have a specific episode info shown for the upcoming episodes? Not sure, but maybe since all the upcoming airings just show Survivor the pvr thinks they are all NEW but different episodes? so it tries to record them all. Not sure this makes sense, but somehow, i think the pvr thinks they are all different NEW episodes. Odd because I have several episodes of survivor still on my 830 pvr and they all have the season/episode number showing, yet the next upcoming survivor episodes do not have the season/episode number showing. I believe something in the background information, is making the pvr believe that these NEW survivor episodes are all different even though they are new, and that is why it would try and record it at the same time on multiple channels. If it was correct, then if you select NEW episodes on HD only, and a show airs on multiple channels at the same time, it will select one channel for you, and if the same episode of the show is on another channel at the same time, you will see that blue symbol telling you that this episode is scheduled to be recorded on another channel. I am assuming that if the episode information for survivor gets updated before next wednesday, the pvr will be smart enough to correct itself and only record the episode on one channel. If not, then maybe just select a specific channel for Survivor and it should help your problem.
Again hope this makes sense, but the problem is certainly in the episode information so that the pvr knows these NEW episodes are all the same NEW episodes.