### 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)

ERR_MAIN_THREAD_GUARD;
	if (use_taa == p_use_taa) {
		return;
	}
	use_taa = p_use_taa;
	RS::get_singleton()->viewport_set_use_taa(viewport, p_use_taa);
}
bool Viewport::is_using_taa() const {
	ERR_READ_THREAD_GUARD_V(false);
	return use_taa;
}
void Viewport::set_use_debanding(bool p_use_debanding) {
	ERR_MAIN_THREAD_GUARD;
	if (use_debanding == p_use_debanding) {
		return;
	}
	use_debanding = p_use_debanding;
	RS::get_singleton()->viewport_set_use_debanding(viewport, p_use_debanding);
}
bool Viewport::is_using_debanding() const {
	ERR_READ_THREAD_GUARD_V(false);
	return use_debanding;
}
void Viewport::set_mesh_lod_threshold(float p_pixels) {
	ERR_MAIN_THREAD_GUARD;
	mesh_lod_threshold = p_pixels;
	RS::get_singleton()->viewport_set_mesh_lod_threshold(viewport, mesh_lod_threshold);
}
float Viewport::get_mesh_lod_threshold() const {