### 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)

for (int i = 0; i < gl_size; i++) {
			bool selected = selection.active && (sel_start != -1) && (glyphs[i].start >= sel_start) && (glyphs[i].end <= sel_end);
			Item *it = _get_item_at_pos(it_from, it_to, glyphs[i].start);
			Color font_color = _find_color(it, p_base_color);
			if (_find_underline(it) || (_find_meta(it, nullptr) && underline_meta)) {
				if (!ul_started) {
					ul_started = true;
					ul_start = p_ofs + Vector2(off.x, off.y);
					ul_color = font_color;
					ul_color.a *= 0.5;
				}
			} else if (ul_started) {
				ul_started = false;
				float y_off = TS->shaped_text_get_underline_position(rid);
				float underline_width = TS->shaped_text_get_underline_thickness(rid) * theme_cache.base_scale;
				draw_line(ul_start + Vector2(0, y_off), p_ofs + Vector2(off.x, off.y + y_off), ul_color, underline_width);
			}
			if (_find_hint(it, nullptr) && underline_hint) {
				if (!dot_ul_started) {
					dot_ul_started = true;
					dot_ul_start = p_ofs + Vector2(off.x, off.y);
					dot_ul_color = font_color;
					dot_ul_color.a *= 0.5;
				}
			} else if (dot_ul_started) {
				dot_ul_started = false;
				float y_off = TS->shaped_text_get_underline_position(rid);
				float underline_width = TS->shaped_text_get_underline_thickness(rid) * theme_cache.base_scale;
				draw_dashed_line(dot_ul_start + Vector2(0, y_off), p_ofs + Vector2(off.x, off.y + y_off), dot_ul_color, underline_width, underline_width * 2);
			}