What's happening before the animation is called by the event? E.g. if the combatant was previously moving, the animator might currently be in transition to the idle animation. Try adding a Wait node (e.g. 0.1 second wait) before the Combatant Animation node.
If your cast animation is played by the cast parameter in your animator controller, try setting up the parameter in ORK's animation setup.
Also, make sure the used combatant's animation System Type is set to Mecanim and uses the correct animation setup (both found at the bottom of the combatant's settings).