Ran one last night and the lightning effects from the Dragon and Giant have been greatly increased, seemed like a dot from the Giant (over 150hp tick) and a 1k + blast from the Dragon, the blast effect seemed to occur when the 2 were together so unsure if link.
Also, unsure if a better tactic would be to prep Truth and Reaver whilst both Lies are still active as I do not believe the effect occured at this point, once prepped to then kill both lies and quickly kill the 2 main bosses!!!! this is just theory but would save a lot of pain as can easily kite the 2 lies for a while.
Would also try and keep the giant on the other side of the arena with 1 person tanking/kiting as effects seemed to happen when were close, but again this is just speculation.