I read about this in another post but it was dated a fews weeks maybe a month ago.

I was playing 3 Normal AI one of each race and me as a Vasari.

When i could finally offer Pirates missions i always sent Moderate or Stronger fleets.

The only enemy left was the other Vasari and he had laided lots of mines. of the 4 planets i could send scouts to all had Pirates fleets haning around with Vasari mines. All 4 planets where dead and totally without structures but the pirates would not leave.

So in short One AI Vasari top of map and me on bottom with a buffer zone of pirates in the middle where no one could clean them out.