Issue #21264: Star Control Quest - Pre-mature completion?
If you finish the (Optional) requirement "clear the galactic zone," it finishes the quest, even if you still have non-optional tasks open.
I had all of the "find X # of star cores in Y zone" tasks still open and in progress, but I killed a robot and so it closed the quest and didn't let me finish those.
In a way I guess it makes sense if taking care of the robots was the end goal of the Star Control questline.
It was mostly annoying because I wanted to use the map markers from the tasks to find all the star cores, and I didn't think that finding star cores should be cancelled out by optionally killing all robots. It was a surprise when the quest closed itself.
So... it may not really be a bug. BUT, I have part two for you:
All of the robots inside the RobCo Battlezone don't count for the requirement "clear the galactic zone".
I had two interior areas left to kill the robots, Nuka Galaxy and Battlezone. I killed the last robot in Nuka Galaxy, and it closed the quest, even though I had not killed all the robots inside the Battlezone.