Okay, this is a weird one. I just went in to do a haven defence mission, released that one of my squad had the wrong ammo in their backpack for their gun and so tried to roll back to an earlier save. Without realising I loaded the ‘Auto save’ rather than my manual save and saw that I’d defeated the attacking force.
It’s been discussed a few times previously, for example:
It’s nice that the save games have such confidence in you though!
Last time I used this “feature” it doubled all my troop’s equipment and gave it to me as a mission reward