### Godot version

v4.0.beta16.official [518b9e580]

### System information

Windows 10

### Issue description

`RichTextLabel` with `threaded` enabled may crash the game or show the following warning if the node is in another scene:

```
W 0:00:03:0802   test.gd:12 @ load_with_scene(): A Thread object has been re-started without wait_to_finish() having been called on it. Please do so to ensure correct cleanup of the thread.
  <C++ Source>   core/os/thread.cpp:76 @ start()
  <Stack Trace>  test.gd:12 @ load_with_scene()
                 test.gd:6 @ load_items()
                 test.gd:26 @ _on_button_pressed()
```

It may crash the game (without any warning) if it's added directly.

In `v4.0.beta15.official [4fa6edc88]` I was able to reproduce the same warning on my project but I can't reproduce it in the attached MRP. I get a different error and will crash too if the node is added directly:

```
E 0:00:03:0019   remove_from_group: Condition "!E" is true.
  <C++ Source>   scene/main/scene_tree.cpp:157 @ remove_from_group()
```


### Steps to reproduce

Click on the  `Load with scene` or `Load with node` buttons in the attached MRP until it shows a warning/error or crashes. It may take a while.

### Minimal reproduction project

[add_chid_bug_b16.zip](https://github.com/godotengine/godot/files/10521402/add_chid_bug_b16.zip)

menu->popup();
			grab_focus();
		}
	}
	Ref<InputEventPanGesture> pan_gesture = p_event;
	if (pan_gesture.is_valid()) {
		if (scroll_active) {
			vscroll->set_value(vscroll->get_value() + vscroll->get_page() * pan_gesture->get_delta().y * 0.5 / 8);
		}
		return;
	}
	Ref<InputEventKey> k = p_event;
	if (k.is_valid()) {
		if (k->is_pressed()) {
			bool handled = false;
			if (k->is_action("ui_page_up", true) && vscroll->is_visible_in_tree()) {
				vscroll->set_value(vscroll->get_value() - vscroll->get_page());
				handled = true;
			}
			if (k->is_action("ui_page_down", true) && vscroll->is_visible_in_tree()) {
				vscroll->set_value(vscroll->get_value() + vscroll->get_page());
				handled = true;
			}
			if (k->is_action("ui_up", true) && vscroll->is_visible_in_tree()) {
				vscroll->set_value(vscroll->get_value() - theme_cache.normal_font->get_height(theme_cache.normal_font_size));
				handled = true;
			}
			if (k->is_action("ui_down", true) && vscroll->is_visible_in_tree()) {
				vscroll->set_value(vscroll->get_value() + theme_cache.normal_font->get_height(theme_cache.normal_font_size));
				handled = true;