Runtime 2.0/2.1 performance dives when rendering multiple 3D scenes on some drivers

A customer pointed out that adding multiple Qt 3D Studio scenes to a QML degrades performance horribly (1scene = 60 fps, 2 scenes = 30 fps etc.) After investigation on my MacBook Pro I noticed that if I run the barrel test scene (from simpleqml example) in multiple instances when connected to external display I can replicate a degradation. Report attached.

Then if I disconnect external devices and sleep the computer I noticed the same test sequence runs at 60 fps all the way through to 10 scenes. It seems this could be caused by the rendering switching from Radeon graphics (with external display attached) to Intel integrated graphics (with no devices attached and after sleep).