You may need to check the VST locations set in Studio One in order for the plug-in to be found in Studio One.
In Studio One go to Studio One > Options (or preferences for Mac) > Locations > VST Plug-Ins. Here you will be able to see the locations set to scan for plug-ins when opening Studio One. You can either add the missing plug-in to the existing directory location or create a new path to where the missing plug-in is currently installed on your computer. The next time you open Studio One the list will scan the locations and update the plug-ins within Studio One.
