With how buggy the recent patch is, I have to wonder if the rupture bugs are actually supposed to be light armor and not medium. Everything about their design is strange. While burrowed, they are very quiet, fast, if not faster than normal, invulnerable to everything except explosives, and have medium armor on top of it. I'm not quite sure what the design philosophy was with them, but I feel like they did not think about how these enemies would fit into the roster, let alone playtest them.
I think they need to either slow them down while burrowed by a large margin, give them light armor instead, or maybe have them stick out of the ground a little, as if they were sharks.