Explanation of the Issue
When using action camera, target an enemy that can normally be targeted by an essence skill. (e.g. the Drakkar stun phase). The essence skill special action will pop up for use, but will fail when activated with the broadcast + chat log message:
Invalid target. Attack a foe imbued with the essence weak to this ability.
This seems to happen either/or when tab-targeting or right-click targeting in action camera, but I haven't been able to confirm what the precise sub-conditions are to trigger the effect. Sometimes untargeting and retargeting works, but often not.