Fighter LVL 10 (Tom Clancy's Ghost Recon: Breakpoint)

In order to get 10lvl, one of the requirements is to kill or SWISS DRB 40 people without dying. I just don't understand how to do it. I killed many times more people from SWISS, no changing weapons, no reboots, no fast travel, no dying, not sitting in a transport, using nothing but SWISS. Tell me, please, if anyone knows. Or is it just a bug that does not count.