I developed with a Reverb G2 for about 2 years, and I remember that there is a lack of clarity about how to properly set up inputs for the controllers, but I can’t remember the specifics and I think it changes depending on which plugins are enabled or not.
Have you seen this: HP Reverb G2 Controllers in Unreal - Mixed Reality | Microsoft Learn
or this: HP Developers Portal | Getting Started with the Unreal Engine 4 Plugin
or this: Windows Mixed Reality, Unreal 5 and HP Reverb G2 headset? - #11 by VictorLerp
Happy to chat further, though I can’t right now, I’ll check one of my 4.27 projects for Reverb G2 inputs to confirm for you what’s working for me.