Wrong Thumb Placement for Meta Avatars after Update to v38 and v40

Hello everyone,

we have been using the Meta Avatars in our projects for the last few months now and after putting in some work we were quite happy with the results. 

However since we recently tried to update from v35.2 to v38 or now even to v40 we noticed a weird displacement in the Avatars thumbs. The thumbs or joints of the thumbs seem to be shifted towards the palm of the hand somehow ( see images for comparison) . It does not hinder the grab functionality - but it makes all hand grab poses look wrong, which renders it unusable for us.

with v35.2

With v38 and v40

I could not find any indication where this is coming from or any way to fix this.

Does anyone have an idea or a tip on how this could be solved?

Additional Information:
Unity 6.2
All-in-One-SDK v78

XR-Plugin: Open XR

We are using an OVRCameraRig with Hands and ControllerDrivenHands.
Hand Skeleton in OVR Manager: Open XR Skeleton