How to improve People Occlusion in ARKit 3.0

Question

We are working on a demo app using people's occlusion in ARKit. Because we want to add videos in the final scene, we use SCNPlanes to render the video using a SCNBillboardConstraint to ensure they are facing the right way. These videos are also partially transparent, using a custom shader on the SCNMaterial we apply (thus playing 2 videos at once).

Now we have some issues where the people's occlusion is very iffy (see image). The video we are using to test is a woman with dark pants and a skirt (if you were wondering what the black is in the image).

The issues we have are that the occlusion does not always line up with the person (as visible in the picture), and that someone's hair is not always correctly detected.

Now our question is what causes these issues? And how can we improve the problems until they look like this? We are currently exploring if the issues are because we are using a plane, but simply using a SCNBox does not fix the problem.