### 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)

charfx->color = font_color;
						bool effect_status = custom_effect->_process_effect_impl(charfx);
						custom_fx_ok = effect_status;
						fx_offset += charfx->offset;
						font_color = charfx->color;
						frid = charfx->font;
						gl = charfx->glyph_index;
						txt_visible &= charfx->visibility;
					}
				} else if (item_fx->type == ITEM_SHAKE) {
					ItemShake *item_shake = static_cast<ItemShake *>(item_fx);
					if (!cn) {
						uint64_t char_current_rand = item_shake->offset_random(glyphs[i].start);
						uint64_t char_previous_rand = item_shake->offset_previous_random(glyphs[i].start);
						uint64_t max_rand = 2147483647;
						double current_offset = Math::remap(char_current_rand % max_rand, 0, max_rand, 0.0f, 2.f * (float)Math_PI);
						double previous_offset = Math::remap(char_previous_rand % max_rand, 0, max_rand, 0.0f, 2.f * (float)Math_PI);
						double n_time = (double)(item_shake->elapsed_time / (0.5f / item_shake->rate));
						n_time = (n_time > 1.0) ? 1.0 : n_time;
						item_shake->prev_off = Point2(Math::lerp(Math::sin(previous_offset), Math::sin(current_offset), n_time), Math::lerp(Math::cos(previous_offset), Math::cos(current_offset), n_time)) * (float)item_shake->strength / 10.0f;
					}
					fx_offset += item_shake->prev_off;
				} else if (item_fx->type == ITEM_WAVE) {
					ItemWave *item_wave = static_cast<ItemWave *>(item_fx);
					if (!cn) {
						double value = Math::sin(item_wave->frequency * item_wave->elapsed_time + ((p_ofs.x + gloff.x) / 50)) * (item_wave->amplitude / 10.0f);
						item_wave->prev_off = Point2(0, 1) * value;
					}
					fx_offset += item_wave->prev_off;
				} else if (item_fx->type == ITEM_TORNADO) {