### 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 (rewrite) {
			for (int j = 0; j < sd_glyphs[i].count; j++) {
				sd_glyphs_new[sd_shift + i + j] = sd_glyphs[i + j];
			}
		}
		if (sd_glyphs[i].count > 0) {
			char32_t c = ch[sd_glyphs[i].start - sd->start];
			if (c == 0xfffc) {
				i += (sd_glyphs[i].count - 1);
				continue;
			}
			if (c == 0x0009 || c == 0x000b) {
				sd_glyphs_new[sd_shift + i].flags |= GRAPHEME_IS_TAB;
			}
			if (is_whitespace(c)) {
				sd_glyphs_new[sd_shift + i].flags |= GRAPHEME_IS_SPACE;
			}
			if (c_punct_size 
				if (u_ispunct(c) && c != 0x005f) {
					sd_glyphs_new[sd_shift + i].flags |= GRAPHEME_IS_PUNCTUATION;
				}
			} else {
				for (int j = 0; j < c_punct_size; j++) {
					if (c_punct[j] == c) {
						sd_glyphs_new[sd_shift + i].flags |= GRAPHEME_IS_PUNCTUATION;
						
					}
				}
			}
			if (is_underscore(c)) {