This is a new game started with the 1.507 release version and the Precursor Worlds DLC
When a race's last remaining planet is a Precursor World, it does not show up properly in the UP Window. I conquered the two normal planets that the race had and left the Precursor World alone while waiting for my culture to flip it.
When I checked the UP I noticed that the race didn't show up correctly. When I clicked on the world of the race, no race information showed up on the right, and the line showing war with me wasn't there. The line did show up when I clicked on Show All, but there was still no race information on the right. Also, I could not double-click on the planet to talk to the race. I could do this with the other races.
A few turns later the race with the problem asked for peace, which I accepted. I checked the UP and found that everything was same as it was when I was at war with them.
Ticket ID #TOB-739-86490