It appears that the Korg Legacy Collection (digital) plugins are not recognized by Cubase Pro 9. These include the M1, Wavestation, and MDXe plugins. Although the .dll files are in the correct VST folder alongside all other .dll files, the plugins do not register on program launch, and are not listed among available VSTs within a session. All of these plugins work fine in 8.5 and earlier.
are they 32bit plugins? if so, cubase 9 blacklist every 32bit vst (then check Korg to see if they have or will release a 64 bit version of them)
They have 64 bit versions, I have it and they work fine.
If your project is currently using the 32 bit version you’ll need to recreate the Instrument with the 64 bit version.
I concur with beerbong, the 64bit version works beautifully with Cubase Pro 9.