Final Coil Turn 2 Add Invincibility

Date & Time: 11/11/2014 12:47 EST
Frequency: Once (Did not reproduce)
Character Name: Liaysa Sineos
Race: Miqo'te F
World: Balmung
Class/Level: Dragoon (50)
Area and Coordinates: Final Coil of Bahamaut Turn 2
Party or Solo: Party (8 Members)
Monster Name: Electric Node

Steps: We progressed through the turn as normal getting into the add phase of this turn, where the 3 ADS adds spawn. We proceeded as usual, killing the Weapons Node and the Security Node at the same time, trying to destory them at the same time. The team on the weapons node was a little bit ahead so I decided to attack the Electric Node to put some damage on it while the rest of my team finished off the 2 other nodes. The weapons node died shortly after me switching targets and the security node came to the electric node, but we destoryed the secuirty node before the Electric node ate it, I know this because we would have wiped there, as the node explodes, killing everyone. Instead the electric node became fully invulnerable after the security node disapeared, and no one could damage the electirc node. It stopped moving totally sat in the same place, not moving and we could not damage it at all, and we were forced to wipe.
We only saw this happen once in the amount of time we were in there. Thank you for reading and I hope this helps.