Plug-ins Loading at the start

How do I stop C8P loading plug-ins that have invalid licences when C8P is first started?

They don’t appear on the main list in the plug-in manager.

As C8P loads, several windows pop-up and I have to select “Quit”

Hello, I really don’t know, but suggest that you also post this at forums where there is intensive usage of iLok dongle’s. Have you tried the SSL forums?

http://www.solid-state-logic.com/support/duende%20native/

Remove the plug-ins from Cubase 8 visibility. The way to do this depends on how you have it setup. If you have copied the .dll files to the Cubase 8 VST Plug-in folder, then just move them somewhere else or delete them. If you have added the file paths to the plug-in information, then you need to remove those paths in the plug-in manager.
HTH
J.L.