Quest2 Touchpad Thumb Touching Query Not Working (Unity)

I'm trying to query the thumb resting on the thumbrest in Unity using the following and it doesn't seem to work:

OVRInput.Get(OVRInput.Touch.PrimaryThumbRest, OVRInput.Controller.LTouch);

I've also tried passing OVRInput.Touch.Any as well and all the other button touch states seem fine. In the dashboard, I'm seeing the ghost hand thumbs rest on the right locations, so I know it's not a controller issue.

I'm definitely in "Quest2" mode, as the headset is reporting back as OVRPlugin.SystemHeadset.Placeholder_9

Any idea why this might not be working for me? 

[Unity 2018.4.26f1, Unity Integration 20.0]