VSTGUI 4.9, PC, 64bit
Cubase displays a white GUI when the VST 2.4 version is loaded. It does not happen with the VST3 version of the plugin. It does not happen in any other host.
Cubase also hides the VST 2.4 version when VST3 is available. You need to delete the VST3 to make VST2.4 appear as a plugin.