I am able to reproduce following Bug 1354630 (using KDE multiple sessions) one again after update to 1.18.4-4.

I'am able to reproduce it on following hardware (Intel-only machine works perfectly as well as VirtualBox F24 KDE-spin setup):

lspci | grep "VGA\|3D"

00:02.0 VGA compatible controller: Intel Corporation 4th Gen Core Processor Integrated Graphics Controller (rev 06)

01:00.0 3D controller: NVIDIA Corporation GK106M [GeForce GTX 760M] (rev a1)

Could be related to prime fixes.

BZ#1368502 Xorg: How to configure?