Hello, a little update on this issue…
I have my Cubase Pro installed on drive Z:, as I use a dual boot system. Now comes the funny thing…I installed Melodyne Studio on my Z-Drive and it does appear as VST3, but not as ARA extension.
So I copied the Celemony/Melodyne/Melodyne.vst3 to my C-Drive, inside the Commonfiles/VST3, and it dos show up now.
I assume, that the araservice.dll only looks at the C-Drive for the extension, but when your system is assigned to another letter, it would not find it…until you move it to the C-Drive.
Hope this helps someone.