I think you said your hissers were males? If so I don't think this is anything to be too worried about - male hissers fight a lot and often clip each others' antennae short as part of the fight. I have a couple of Elliptorhina javanica males which now have little more than stubs for antennae, as they are always fighting, and they seem otherwise to be perfectly healthy - it doesn't seem to stop them feeding or otherwise getting around OK so I think your hisser will be perfectly fine.
Not sure why they do this, I read somewhere it could be that rival males clip the antennae of their "opponents" to stop them smelling out a female so effectively, but I don't know if that's true or not!