### Godot version

4.2 eca6f0e

### System information

Windows 10 x64

### Issue description


https://github.com/godotengine/godot/assets/2223172/a2796263-4e2e-4b14-a080-b3ad034cc141



### Steps to reproduce

1. Add SubViewport
2. Add Sprite2D
3. Set spirte's texture to ViewportTexture
4. Create new scene
5. Instance the new scene inside the scene with viewport
6. Make sure both scenes are opened
7. Go to instance scene and save it
8. Go to viewport scene

You will see error spam. Reloading the scene fixes it.

### Minimal reproduction project

[vip.zip](https://github.com/godotengine/godot/files/12292386/vip.zip)

_drop_physics_mouseover();
		}
		gui.mouse_over = over;
		if (over) {
			over->notification(Control::NOTIFICATION_MOUSE_ENTER);
			notify_embedded_viewports = true;
		}
	}
	if (over) {
		SubViewportContainer *c = Object::cast_to<SubViewportContainer>(over);
		if (!c) {
			return;
		}
		Vector2 pos = c->get_global_transform_with_canvas().affine_inverse().xform(p_pos);
		if (c->is_stretch_enabled()) {
			pos /= c->get_stretch_shrink();
		}
		for (int i = 0; i < c->get_child_count(); i++) {
			SubViewport *v = Object::cast_to<SubViewport>(c->get_child(i));
			if (!v || v->is_input_disabled()) {
				continue;
			}
			if (notify_embedded_viewports) {
				v->notification(NOTIFICATION_VP_MOUSE_ENTER);
			}
			v->_update_mouse_over(v->get_final_transform().affine_inverse().xform(pos));
		}
	}
}
void Viewport::_mouse_leave_viewport() {