I’ve just tried this with Kontakt Player 6 and it loads for me without problems. Dorico already whitelists ‘Kontakt5 16 Out’ and ‘Kontakt’ so you shouldn’t need it in your own whitelist file.
I’d suggest:
- copy your current whitelist file and edit it to remove the Kontakt entries from it
- delete C:\Users{username}\AppData\Roaming\Steinberg\VSTAudioEngine3_64 directory
- start Dorico again so it recreates the default configuration
- Open a project in Dorico then in Preferences > Play edit the VST plugin paths again to add C:\Program Files\Native Instruments\VSTPlugins 64 bit
- Restart Dorico