I've been unable to call Trooper Squads at all, claiming I have hostile visitors. I don't know if it's related, but I'm mostly noting that there is some bugginess with the Unit Summoning permits.

note that there is a correct implementation of this in the code you should check for to bug report this: specifically, this message is used to handle cases where you are about to summon a trooper squad to engage *your own allies*, who are hostile to the Empire but not to you.

In those cases, the trooper squad will not summon, but if raiders appear on the map at the same time, you can summon them once more - that is, the message appears when the only targets the trooper squad would engage are friendly to the player.