Cubase 9 disables Ozone 4 in my projects and won’t allow it to be reactivated. This pleases me not. 
Hey smokeAndMirrors you are on Windows, correct? I checked it on my machine with Ozone 4: the blacklisted dll is a helper dll and not a valid plugin (“iZOzone4.dll”). Ozone 4 is available in Cubase 9 (“iZotope Ozone 4.dll”)