Hmmm can_force_invade would only apply to if there was something forcing the AI to invade though? I don't see something in the code calling for that when not at war with a faction or being overwhelmed.
At the same time, council missions are never aggressive towards nations at war (at least not for the player). But then maybe there is something in the hardcode we don't know about (random port blockading of an ally for a turn for example)