Hi @KronKrian thanks for the report. If you have a save from before you encounter the fortress, that would be very helpful. Otherwise, I will try to reproduce the issue and add it to our database.
On the matter of the AI colonizing the system, we aware of this being a potential issue and have a fix for that in our internal build.
On the matter of the AI colonizing the system, we aware of this being a potential issue and have a fix for that in our internal build.