### 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)

ERR_FAIL_COND(p_event.is_null());
	Ref<InputEventMouseButton> b = p_event;
	if (b.is_valid()) {
		if (b->get_button_index() == MouseButton::LEFT) {
			if (b->is_pressed() && !b->is_double_click()) {
				scroll_updated = false;
				ItemFrame *c_frame = nullptr;
				int c_line = 0;
				Item *c_item = nullptr;
				int c_index = 0;
				bool outside;
				selection.drag_attempt = false;
				_find_click(main, b->get_position(), &c_frame, &c_line, &c_item, &c_index, &outside, false);
				if (c_item != nullptr) {
					if (selection.enabled) {
						selection.click_frame = c_frame;
						selection.click_item = c_item;
						selection.click_line = c_line;
						selection.click_char = c_index;
						
						if (selection.active) {
							if (_is_click_inside_selection()) {
								selection.drag_attempt = true;
								selection.click_item = nullptr;
							} else {
								selection.from_frame = nullptr;
								selection.from_line = 0;