Some array elements do not engage in newly chunked, different string length element array : I am trying to convert a string array into new string array, changing the word count of each elements by appending sibling items accordingly. But the problem I am having is some part of previous array is not converting as required. 

**Here is my code so far :**
```
$text_array = ['He needs to cultivate in order', 
'to be at the fourth level of the', 
'Martial Body Stage. Does he have inner energy?"', 
'Everyone jeered, laughed, and taunted.', 
'Qin Yun turned deaf ear to their taunts.',  
'His eyes were filled with sincerity as he',  
'looked at Yang Shiyue and said, "Teacher,', 
'I only formed my elemental energy this morning.', 
'I still not familiar with the control of', 
'my elemental energy and inner energy."',  
'After the empress heard the jeers from the',  
'crowd, she let out a sigh of relief and',  
'sneered, "This is only a little bit of',  
'inner Qi that you forced out.', 
'You have not yet stepped',  
'into the fourth level',  
'of the Martial Body realm and have no',  
'chance of breaking through. embarrass yourself!'];

        $last_converted_index = 0;
        $new_string_array = [];
        $single_valid_length_string = '';
        foreach (array_slice($text_array, $last_converted_index) as $item) {

            if (str_word_count($single_valid_length_string . $item) < 30) {

                $single_valid_length_string .= $item . ' ';
                $last_converted_index++;

            } else {
                $new_string_array[] = $single_valid_length_string."<br><br>";
                $single_valid_length_string = '';
            }

        }

        echo implode($new_string_array);
```
  Any help would be appreciable.