Bones move to unexpected position during motion capture

Please forgive my lack of knowledge; I am immensely new to 3D modeling. I currently have a rigged model in Blender, which was exported from Adobe Mixamo as a FBX and brought into Blender. My end goal is to use this model with Apple’s AR Body Tracking technology.

When I export the model as a FBX, convert to a USDZ (as required by Apple), and load into my app, the model appears as expected. When I attach the model to a tracked body, however, some of the joints affix themselves to bizarre positions. Per the attachment, you can see that the arms appear to be tracking properly, but the left leg is barely moving and is facing the wrong direction.

Could there be any suggestions of why the model seems to look and react normally in Blender, but such behavior occurs on the Apple side of things?

What I see in Blender;

What happens with Motion Tracking;

Thanks very much!