Update: Still not working 
Tried another two fresh installs.
Nothing seems to be triggering the scanning of VST3s.
Tried with disabled preferences during startup and also tried removing any user profiles. Although I could get VST2s to rescan every time after a fresh install, VST3s just won’t scan.
When checking the plugin-in manager and sorting it by VST Version, you can clearly see that all stock Steinberg VST3s load properly, followed by all my 3rd party VST2s. (See screenshot)
The default plugin paths for VST3 are where my VST3 plugins reside (See screenshot)
As for now, everything works as expected on C11.5. So work can still go ahead but its only fair I’m more than excited to try out C12 
Hoping for a fix soon! In the meantime, I’ll keep trying!