Do you have the correct paths to your VST folders set up correctly under Preferences → Plug/Misc?
Under Windows, installers install VST2 plugins automatically to different locations. Unless a user is always vigilant and tries to always make sure that plugins are installed in one common place, it is likely that the user may have plugins installed all over the place. I’m not sure if this is an issue for Mac users.
Also, I thought that Renoise could bridge 32-bit plugins. Is that no longer the case?