“Duplicate copies of the track cannot be edited.” Correct. It is organised in folders. To clone a track from another user, copy to a track outside that folder.
Don’t know what your Nexus problems are all about, VST Transit just remembers the plugs name and ID and attempts to re-build the tracks as they were sent. “that the synth had been cleared from the track allocation during transfer” - you mean the inserted instrument would not show? Could be there are different versions of that plug on both sides?