I just discovered that choosing a custom path for installing problems can prevent Cubase from loading VST3 versions.
In this case it was Valhalla VintageVerb. I could not figure it was only showing VST 2.4 until I reinstalled and used the default folder, in this case:
C:\Program Files\Common Files\VST3
The screenshot shows VST 2.4 versions loading as they are in my C:\Audio\Plugins\Valhalla folder.
I had/have a very similar problem with Slate FGX not showing up in Wavelab and Sound Forge, it seems to be some issues regarding 32/64 bit versions and the location.