I also believe that the vraysun is the problem.You are using the vray dome light and the vray sun as light sources and the vrayhdri mtl as environment background.I suggest that you turn off the vraysun and if you still have the same problem, modify in photoshop the exposure of the sun of the hdri. You can do it in low 32 bit exposure by selecting the sun and adjusting the exposure of the selected area.