Dedra is not Undermining allies who trigger Expose on their turn

In the Coliseum against Jotaz and Pirate AT-ST the Hero Ability is active. Thus the boss keeps getting Exposed. Every turn allies damage the boss, and despite that, they are not getting Undermined by Dedra.

In the attached video, both the Death Trooper and Krennic should be getting Undermined as they triggered the Expose on the AT-ST during their turn, but they're not.