Summary: I'm assuming when at war with the Battanians in my playthrough, there was an attempt to siege Sargot. Although, this failed as it was never taken, although the icon to display the siege is there, even after the siege was broken and peace has been made. See image below for more info.
How to Reproduce: Attempt to siege the settlement and break a siege? I'm not too sure.
How to Reproduce: Attempt to siege the settlement and break a siege? I'm not too sure.