When two or more diver units are in scene, the shadowvolume mesh breaks.
Tested in current dev branch and diag exe.
Two units side by side:

As i pan the camera to the left and another diver is being rendered the shadows for the diver break (note that the shadows for the diver's fins reappear incorrectly):

Here with the diver closer, the second diver' shadow seems to be working correctly here:

Could be replicated from different angles, here is what it looks like in diag exe with drawmode "shadowvolume":