### 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 (subtag_a.size() == 2) {
					if (subtag_a[0] == "expand") {
						int ratio = subtag_a[1].to_int();
						if (ratio < 1) {
							ratio = 1;
						}
						set_table_column_expand(get_current_table_column(), true, ratio);
					}
				}
			}
			push_cell();
			const Color fallback_color = Color(0, 0, 0, 0);
			for (int i = 0; i < subtag.size(); i++) {
				Vector<String> subtag_a = subtag[i].split("=");
				if (subtag_a.size() == 2) {
					if (subtag_a[0] == "border") {
						Color color = Color::from_string(subtag_a[1], fallback_color);
						set_cell_border_color(color);
					} else if (subtag_a[0] == "bg") {
						Vector<String> subtag_b = subtag_a[1].split(",");
						if (subtag_b.size() == 2) {
							Color color1 = Color::from_string(subtag_b[0], fallback_color);
							Color color2 = Color::from_string(subtag_b[1], fallback_color);
							set_cell_row_background_color(color1, color2);
						}
						if (subtag_b.size() == 1) {
							Color color1 = Color::from_string(subtag_a[1], fallback_color);
							set_cell_row_background_color(color1, color1);
						}
					} else if (subtag_a[0] == "padding") {