Comment # 3 on bug 1110985 from Stefan Dirsch

Ok. This is still Ivybridge. Since you said yourself this still worked on TW
previously using the Intel SNA driver, it would be worth a try to install
xf86-video-intel package on your freshly installed TW. If this doesn't help,
this looks like a regression in the kernel driver.

Or with Plasma we now have completely different requirements for the desktop
WRT 3D acceleration, so trying to use Cinnamon desktop again might be the first
option.