The SteamVR plugin has been deprecated, it’s unlikely Epic will fix any bugs in it.
For the OpenXR plugin, one common possible cause for the inputs not working is the runtime not transitioning into the FOCUSED session state. This can happen either because the SteamVR Dashboard is open, or if the proximity sensor on the headset is not activating. You can force SteamVR to ignore the proximity sensor by going into the SteamVR settings and turning off the option Video → Pause VR when headset is idle.