did you add binding for knuckles? Window -> Steam VR Input -> Input Bindings then change the selected controller to knuckles and configure it. Make sure to clock Replace default bindings when done.
Viewing post in Help with issue with built game on valve index
I think I know what you mean but I'm not using the SteamVR Plugin, was that something I needed to use to make it compatible with the valve index? I did everything I needed to do with the OpenXR Plugin and didn't have to configure any bindings like that for the Vive controllers, just reference 'trigger' and 'grip' on the XR controller components.