A Female Striker Bug
Unequipped everything to show that it's not a gear thing.
Something is hitting enemies when Striker moves past them. It does no damage, but you can clearly see the Sandbag flinch as if it were hit.
Even walking triggers it, so it's not Stampede related. (You can even see whatever it is "Missed!" the first time I walked by.)
It only happens once per enemy.
Not sure what's going on.