How to sync ARFrame & ARFaceAnchor geometry ?

Hi,
I'm using ARSCNView's delegate(ARSCNViewDelegate) to receive SCNNode(ARSCNFaceGeometry) updates.

I've observed cases where the face geometry (blink detection) misses by 1 frame.

I detect this case by visually comparing the image and the mesh in the method:
Code Block  
renderer(_ renderer: SCNSceneRenderer, didUpdate node: SCNNode, for anchor: ARAnchor)


I pull the ARFrame from (renderer as?ARSCNView).session.currentFrame

My question is:
Is it guarantied that the session.currentFrame in the renderer:didUpdate scope to be always in sync with the face geometry?

I suspect a potential problem here since the geometry is being "pushed" while the current frame is being "pulled".