An update on this. In a non-raid party, people seem to disappear from frame 1 at random and having show duplicates doesn't seem to matter. I don't have "hide bars for out of range" on either.
Another odd thing I've noticed which is likely related is that I have highlights for buffs on the MT frame (but not frame 1), but private tanks who are missing the buff that are incorrectly in frame 1 still get highlighted.
If I have some time this weekend I will try to reset my settings and see if I can reproduce.
Also worth noting that I tried using the built-in 40-man test bars, I was not able to reproduce this behavior. I also tried the new toggle to turn main assist inclusion as a main tank option both on and off, and it didn't seem to make any difference.
This isn't a full bug report yet as I am wary of completely resetting my HB settings to test it out, but I thought I'd add a description and see if anyone else is having this problem which started occurring for me within the last couple weeks.
Frame 1 is set to be the raid+party+self, Frame 2 is set to be Main Tanks+private list, I don't have allow duplicates on. I also have pets in a separate frame.
It seems tanks/private tanks/permanent private tanks don't show up in Frame 2, but stay in Frame 1 at random now. I can't find any rhyme or reason as to what causes them to switch, but throughout raids it appears different people get swapped in and out.
After the raid last night I spent some time trying to hammer it down, and found some weird behavior. I unchecked everything from the Frame 1 group except "self" but it still showed both my character and one of the main tanks. If I uncheck "self" both characters disappear, recheck and they both show up.
Should I spend the time to do a full reset or has something in this area of the code been changed recently?