It’s possible for the Chaos Spawn to grab an Ironbreaker with Gromril Curse, which can instantly kill the IB but break the Chaos spawn AI where it can no longer attack.
Ironbreaker with Gromril curse is the one consistency I noticed every time I saw this happen. It might be knockback related though (instead of only Gromril curse) in which case it could be possible with other careers as well.
