Goliath while falling, even from a small ledge.
Kraken and EK while freefalling if traversal is run out and connecting with level geometry (puts Monster in freefall).
Berb while fall/rolling off ledges.
Monsters in freefall are “knocked back” by EMET’s rockets, causing monster to float in the air and lose movement control.
No video at this time.
However, other users are reporting this bug as well: