In lieu of a proper answer to your issue - I haven't tried to add plugs with the faderport - I have a suggestion for you.
If you have a tablet computer (Android, Microsoft or iOS) you can use the Studio one remote app to drop plugins onto a channel. I know this is not the most ideal way, however iI have had some pretty good results.
Use the tablet to drop the plug and the faderport to edit them. You can select the track with the fp, drop plug using the app, presto voila.
Sorry I can only offer a workaround.