Under 390.48 everything worked well in Blender and having duo Intel-nVidia I could work under Intel by prime-select and have nVidia activated in Blender. After update to 396.24 there's no cuda found and even I go back to 390.48 it's still the issue. Even I will switch to nVidia entirely by prime-select nvidia the cuda still isn't detected. I wonder if there may be other areas of ubuntu internal or other apps/dependencies which could break nVidia cuda detection? Any version of Blender checked. No any major ingerentions made in system internally just standard updates coming daily.
SnapOverflow
Do you have the nvidia-cuda-toolkit package? If not type the following into terminal:
I have found that the default repository version of blender in Ubuntu does not contain precompiled cuda kernels, and thus requires
cuda-toolkitto enable GPU rendering.Installing blender from Thomas Shiex's ppa however pulls precomplied cuda kernels so you can avoid the initial kernel compilation as well as the installation of cuda-toolkit.
If you've just updated ubuntu your ppa should have been disabled and your blender has been probably replaced by the official ubuntu package, thus "removing" cuda support if you don't have cuda-toolkit already installed.