Best work around i have found is opening a plugin via the VST rack instead of the instrument track. Clicking on the name in the inspector as suggested above did nothing- this was one of the first things i tried before i posted.
To clarify, you need to click in the output selection box in the inspector. This is just under the midi inputs and above the midi channel selection. It will open the drop down instrument selector.
Maybe you are clicking on the main heading which doesn’t do anything?
If this doesn’t work for you then there is something wrong with your installation.