Instead of capturing a colony, I wanted to completely bomb it out of existence. Specifically an orbital habitat. Oddly I was able to do so with one of them but couldn't with two others. My fleets just orbited instead of opening fire. I also bombed two planets into tomb worlds.
I tried different bombardment stances as well as changing targets. Those specific habitats couldn't be bombarded. To reiterate, my fleets simply orbited without firing a shot.

Any idea why that is?