Scene Widget hiddes when clicking the window

### Checklist

- [x] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [x] For Python issues, I have tested with the [latest development wheel](https://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [x] I have checked the [release documentation](https://www.open3d.org/docs/release/) and the [latest documentation](https://www.open3d.org/docs/latest/) (for `main` branch).

### My Question

Hi all!,

Im a really really new with Open3D im trying to create a prototype for my company to visualize a Sonar Point Cloud Scan. I manage to work with the visualizer but i want to add some complex functions so i changed to the GUI (way more complex haha).

For sure i cannot copy and paste the whole code but i have really trouble to manage putting together Vert, Horiz, SceneWidget, etc.

I kind of understand how its organized the Vert, Horiz and other gui option but my main issue that i have a Vertical where at the top i place a Horizontal and the a SceneWidget and when i click the window the SceneWidget BOOM, dissapears. I dont really know if im missing something, i literally search for ever and nothing usefull.

Just for context im using Open3d 0.19, Qt 6.9.1 MSCV2022

`
auto window = std::make_shared("Bathy-3D", 1920, 1080);
auto scene_widget = std::make_shared(displayedCloud);
auto main_layout = std::make_shared(0, open3d::visualization::gui::Margins(5));
auto stats_layout = std::make_shared(10, open3d::visualization::gui::Margins(10));

main_layout->AddChild(stats_layout);
main_layout->AddChild(scene_widget);
window->AddChild(main_layout);

`

Please if you have any idea why or you want to ask anything. I will be here

Thanks to the community :)