I found what I assume is an NPR, except the NPR has literally zero building on its homeworld. It has 1070 million people on the planet, but no buildings. I used an Elint ship in orbit to find that they had 1070 million population but no facilities, and then invaded the population, and they had no ground units, so I used SM to spawn in a giant (7 million PWL infantry) formation to force the population to surrender despite the 100x strength needed to surrender bug. At which point, I confirmed that there was literally zero facilities on the planet, not even conventional factories.
Possibly relevant information:
I had a elint/diplomatic ship in orbit for a while, but eventually left only an Elint ship in orbit.
I never received any messages from them despite having ships in orbit of their homeworld. Turning on the Transponders on my ships did not do anything.
I started the game with 2 billion population on my capital instead of 500 million
There was a precursor ground army on the 4th planet of the system the NPR was in. The precursor army did have STO weapons, but I destroyed them.
Database file is attached, the aliens are in the system of Seabring, on the second planet.