Rebelling units.
Rebelling units attack other units and core. Attacked units do not respond in any way and get angry themselves. Eventually they also rebel which keeps going on until all creatures rebel and destroy the core.
Suggestion 1 : Rebel units change their faction, thus become targetable by your creatures.
Suggestion 2 : Rebel units try to leave your dungeon through portal, if they can't, they start slowly lose health while keep attacking everything and everyone. Eventually they just die out of ''hunger''.
Oh I forgot to answer the ticket.
So there was just a slight logical fail (a missing brace) in an ally-check which prevented other units from attacking rebelling units.
Now it works as intented, which is: A rebelling unit is allowed to deal the first hit, before it is demasked as an enemy. After the first of your units got any hit from the rebelling unit, every of your own units will fight back.
This is to make it look more interesting than just directly attacking a rebelling unit.
If the rebelling unit does not find other units to attack in view range, it will always try to find a gateway to leave your dungeon.