I am also encountering this bug, after upgrading from Kubuntu 17.10 to 18.04.
For me, initially only my Intel driver wouldn't work (with PRIME) - it would instead just go ahead and use the NVidia driver (even when PRIME said Intel was in use).
However, upgrading to {xserver-xorg-video-nvidia-396,nvidia-driver-396,nvidia-utils-396} via the graphics-drivers ppa results in neither operating correctly and the fallback llvmpipe software renderer being used.
I am also encountering this bug, after upgrading from Kubuntu 17.10 to 18.04.
For me, initially only my Intel driver wouldn't work (with PRIME) - it would instead just go ahead and use the NVidia driver (even when PRIME said Intel was in use).
However, upgrading to {xserver- xorg-video- nvidia- 396,nvidia- driver- 396,nvidia- utils-396} via the graphics-drivers ppa results in neither operating correctly and the fallback llvmpipe software renderer being used.