### Godot version

master ([06ccbfe](https://github.com/godotengine/godot/commit/06ccbfe8eec6e840db3df2360dc2804386f940b8))

### System information

PopOS 22.04

### Issue description

Sometimes the doc page is broken when the engine is closed and then restarted.
Closing the doc and opening it again fixes it.

![2023-05-27_22-15](https://github.com/godotengine/godot/assets/3624853/ed202a55-03e8-420a-bc1c-ccfc7f7cd02a)


### Steps to reproduce

- Open a documentation page for any node
- Restart Godot

### Minimal reproduction project

NA

EDIT : Added the commit hash @Calinou 
_stop_thread();
	MutexLock data_lock(data_mutex);
	ItemCustomFX *item = memnew(ItemCustomFX);
	item->custom_effect = p_custom_effect;
	item->char_fx_transform->environment = p_environment;
	_add_item(item, true);
	set_process_internal(true);
}
void RichTextLabel::set_table_column_expand(int p_column, bool p_expand, int p_ratio) {
	_stop_thread();
	MutexLock data_lock(data_mutex);
	ERR_FAIL_COND(current->type != ITEM_TABLE);
	ItemTable *table = static_cast<ItemTable *>(current);
	ERR_FAIL_INDEX(p_column, (int)table->columns.size());
	table->columns[p_column].expand = p_expand;
	table->columns[p_column].expand_ratio = p_ratio;
}
void RichTextLabel::set_cell_row_background_color(const Color &p_odd_row_bg, const Color &p_even_row_bg) {
	_stop_thread();
	MutexLock data_lock(data_mutex);
	ERR_FAIL_COND(current->type != ITEM_FRAME);
	ItemFrame *cell = static_cast<ItemFrame *>(current);
	ERR_FAIL_COND(!cell->cell);
	cell->odd_row_bg = p_odd_row_bg;
	cell->even_row_bg = p_even_row_bg;
}
void RichTextLabel::set_cell_border_color(const Color &p_color) {