I experience this issue and I figured it out. You have to do this to activate both EZMIX & SUPERIOR DRUMMER the first step is Superior drummer the second is EZMIX. I am assuming you can do the same for EZKeys and any other plugin not installed.
Open Studio one
at the top menu option click on STUDIO ONE then click on OPTIONS then LOCATIONS then INSTRUMENT LIBRARY then ADD check the directory for:
C:\Program Files\Common Files\VST3
Then Select VST Plug-Ins then ADD Then
C:\Program Files\Common Files \VST3
Close down Studio One and Open it again. It should load everything!
Good Luck to All!