Would post in the bug report forum, but I can't due to being on probation 
I've run two observer games so far that have both seen the Unbidden show up. They always stall after destroying a system or two and just seem to sit around. Even after their constructors have built their military stations and are sitting around with no orders, they do nothing.
However, if you save the game and then reload that save, the Unbidden suddenly spring to life and get back to work, even though it's exactly the same date on the in-game clock.
I've run two observer games so far that have both seen the Unbidden show up. They always stall after destroying a system or two and just seem to sit around. Even after their constructors have built their military stations and are sitting around with no orders, they do nothing.
However, if you save the game and then reload that save, the Unbidden suddenly spring to life and get back to work, even though it's exactly the same date on the in-game clock.