GSF, I don't have answers. I call it PASSIVE robbing when the bees don't fight. Easy to spot as the robbers leave the hive being robbed with elongated abdomen, full stomachs. Bees leaving a hive usually have short (empty) stomachs. I've seen bees tear apart each other, relentless almost cruel behavior. Then I have seen rogue queens march into a queen right hive no problems and take over the hive. The original marked queen, a good layer, cannot be found, I assume killed by the rogue. Go figure???
Maybe Iddee and his decades of experience will have some answers. Glad your health is improving Iddee.