Having recently upgraded to Cubase AI 10 I have been pulling my hair out since I could not get any input to register. Long story short, after trying out different port mappings and swapping in a different interface, I finally found that this behaviour is caused by the microphone security settings. If you run into this problem, make sure that Cubase is allowed to access the microphone, since without it you will get no input from an interface at all.

To check, go to ‘Preferences’ – ‘Microphone’ – ensure that Cubase has a tick in front of it.