Re-opening sessions using VEP

Just bought and started using Vienna Ensemble Pro.
Works exactly as advertised - amazing piece of software.

My setup is Cubase 9.5 on a Win 7 PC and running the server on a Mac mini.
I have one instrument track assigned to the plugin - all the tracks with midi are then assigned to that instance of VEP.

When I save my Cubase session everything is assigned and working but when I reopen, I have to re-assign every track assigned to the VEP plugin.
Obviously doing something wrong.