With having multiple Archon Shadow Priests, seems like Resonant Energy is not working correctly and only 1 debuff is shown on the mob. Unsure if this is applying the damage increase for other priests, but a bug either way.
This was changed recently and now it is only allowing 1 Priest to apply Resonant Energy. If multiple Priests try the 2nd one will never apply. Unsure if the damage increase is shared between people but either way definitely bugged.