Exact same thing happened to me, until it didn't. Haha, I say that because I don't know what I did to get it to work but when I pulled up Luke Cage and didn't see DV, I did a search on HDR in Netflix, click on Iron Fist, and it was the same deal. I then pulled up Netflix on WebOS, and saw DV on Luke Cage. I went back to Netflix on the ATV, right clicked on the DV banner when it popped up on the top right corner, it highlighted in red. I then went back to Luke Cage and bam there it was. I also confirmed Iron Fist, and Defenders.
I'm not sure what made it show up, but those are the exact steps I took.
Oh, I'm set up as 4k DV 24Hz