So recently, I shared a Lobby test with few friends, but on one of the friend's PCs, it sucked up 90% GPU power (and his PC aint' no potato)
It was an empty 3D scene, with some basic main menu GUI linked to edited version of Code Monkey's lobby tutorial script (first time I am doing networking in unity)
On like other 3 PCs everything ran fine. I even tried sending him a build where FPS was limited to 60 and Vsync turned off.
I am not really sure how to detect/fix where the problem is.
(ping me if you respond)