Ah ok, so there’s a chance that you’re copying mappings from older versions of the plugins you have perhaps? I’ve had this issue with Synthmaster VST before. The parameters display on the screen because of the text assigned to them, but the actual Parameter ID’s have changed in the plugin following an update.
Personally, i’d try to create a basic mapping in Nektarine, confirm it works with your P, and then copy it using the folders i’ve stated above and check within Cubase transparently.