Thanks Shayne, this code saved my project.

The code is outdated though if you are using OpenXR. There's now a better way to compute the QR Code's pose. For QRCodeInformation, I'm adding another field called "SpatialGraphNodeID":

public class QRCodeInformation
{
    public string Data { get; set; }
    public float Length { get; set; }
#if WINDOWS_UWP
    public SpatialCoordinateSystem QRSpatialCoordinateSystem { get; set; }
    public Guid SpatialGraphNodeID { get; set; } 
    public QRCodeInformation(string data, SpatialCoordinateSystem qrSpatialCoordinateSystem, float length, Guid spatialGraphNodeID)
    {
        Data = data;
        Length = length;
        QRSpatialCoordinateSystem = qrSpatialCoordinateSystem;
        SpatialGraphNodeID = spatialGraphNodeID;
    }
#endif
    public QRCodeInformation() { }
}

I had to change some code to match the new constructor's signature.

Then, to find the pose, I use this code instead:

SpatialGraphNode node = SpatialGraphNode.FromStaticNodeId(SpatialGraphNodeID);
        Pose pose;
        if (node != null && node.TryLocate(FrameTime.OnUpdate, out pose))
        {
            if (CameraCache.Main.transform.parent != null)
            {
                pose = pose.GetTransformedBy(CameraCache.Main.transform.parent);
            }
            marker.transform.SetPositionAndRotation(pose.position, pose.rotation);
        }

This snippet is from: Microsoft' QR Source Code

I hate making public posts very much. However, I think this would be a very good PSA for anyone who's about to go Kylo Ren on their equipment.

PS: I could clean up your code to remove any WinRT reference too, but I just have no fight left at the moment.