Switch the property "ar-placement" from "floor" to "wall" after entering the webXr mode

### Description

Following the first example of the WebXR demo (https://modelviewer.dev/examples/augmentedreality/index.html), I can switch the src of the model while inside the WebXR view.
Now I'm trying to also update the ar-placement property for each object (from floor to wall, depending on the object), but I found out that after entering in the WebXr mode, the shadow updates correctly, but the ar placement in the room is not updated in the right way.
If I leave the webxr mode, and come back, it updades correctly but only on the first one (the one in the view), not the others.

### Version
- model-viewer: v3.0.2

### Browser Affected
- [X] Chrome, version: 110.0.5481.154

### OS

- [X] Android, version: 13

### AR

- [X] WebXR