### 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)

if (feature_sets.has(p_name)) {
		return feature_sets[p_name];
	}
	
	return hb_tag_from_string(p_name.replace("custom_", "").ascii().get_data(), -1);
}
Variant::Type TextServerAdvanced::_get_tag_type(int64_t p_tag) const {
	if (feature_sets_inv.has(p_tag)) {
		return feature_sets_inv[p_tag].vtype;
	}
	return Variant::Type::INT;
}
bool TextServerAdvanced::_get_tag_hidden(int64_t p_tag) const {
	if (feature_sets_inv.has(p_tag)) {
		return feature_sets_inv[p_tag].hidden;
	}
	return false;
}
String TextServerAdvanced::_tag_to_name(int64_t p_tag) const {
	if (feature_sets_inv.has(p_tag)) {
		return feature_sets_inv[p_tag].name;
	}
	
	char name[5];
	memset(name, 0, 5);
	hb_tag_to_string(p_tag, name);
	return String("custom_") + String(name);
}
_FORCE_INLINE_ TextServerAdvanced::FontTexturePosition TextServerAdvanced::find_texture_pos_for_glyph(FontForSizeAdvanced *p_data, int p_color_size, Image::Format p_image_format, int p_width, int p_height, bool p_msdf) const {