I used a slow on Orfen and he was in the air (he moved upwards). Now it is impossible to attack (Target is too far). Apparently this is some kind of bug Sea of Spores, because there are other mobs hanging in the air.
As it turned out, the slow has nothing to do with it. In Sea of Spores there are big problems with the geodata. It happens that you just walk around the location and find yourself in the air, from which there is no way to get out except SoE.