I think I've found a Lens bug that manifests itself only on-device (not in Lens Studio): the orthographic camera, which is set to render a layer called "Orthographic", renders "Default" layer content. For example, I have a 3D model on the Default layer and a UI element (a 2D image) in the orthographic layer. Initially, Lens Studio places the ortho camera off to the side in world space but if the 3D content makes it over there, it will be rendered on-screen with an ortho projection.
This is not reproducible in Lens Studio but happens in Snapchat only. The easiest way to test this is to move the ortho camera to the same position as the default scene camera so that when the lens runs, the 3D content is simultaneously in the both frustums. You will see the 3D content rendered normally and another copy overlaying it but pinned to the screen with an orthographic projection.
Is there any workaround? I can place the camera really far away but I am concerned that there might be pathological cases where the SLAM system loses tracking and repositions itself near the ortho camera, as unlikely as that may be.