IEnumerator's did not read "bool" after yield return new WaitForSeconds.

Hi, I started using Unity in early March 2020 and trying out coroutine. Im working on a tower defense game, most of the code are base on Brackey's tutorial.

In the script there are suppose to have 3 types of orcs(speed, common, tank). They are spawn in orders (from "SpawnWaveSpd" to "SpawnWave" to "SpawnWaveTank").

I use bool to keep track which type of orc is spawning and which is not. The SpawnWaveSpd's bool (spdOrcIsSpawning) & Spawnwave's bool (comOrcIsSpawning) is working fine. Only when it comes to the end, the SpawnWaveTank's bool (tankOrcIsSpawning) keep at "true" after complete spawning.

Am I doing it right or is there something Im miss out?

 //Speed Orc spawn 1st
     IEnumerator SpawnWaveSpd(Wave _wave)
     {
         state = SpawnState.Spawning;
         spdOrcIsSpawning = true;
 
         for (int i = 0; i < _wave.countSpd; i++)
         {
 
             SpawnSpdOrc(_wave.enemySpd);
 
             yield return new WaitForSeconds(0.5f / _wave.rate);
 
         }
 
         spdOrcIsSpawning = false;
 
         yield return StartCoroutine(SpawnWave(enemyWaves[nextWave]));
 
     }
 
 
 //Common Orc spawn 2nd
     IEnumerator SpawnWave(Wave _wave)
     {
         
         comOrcIsSpawning = true;
 
         for (int i = 0; i < _wave.countCom; i++)
         {
 
             SpawnOrc(_wave.enemyCom);
             yield return new WaitForSeconds(0.5f / _wave.rate);
 
         }
 
         comOrcIsSpawning = false;
 
         yield return StartCoroutine(SpawnWaveTank(enemyWaves[nextWave]));
     }
 
 
     //Tank Orc spawn last
     IEnumerator SpawnWaveTank(Wave _wave)
     {
         tankOrcIsSpawning = true;
 
         for (int i = 0; i < _wave.counttank; i++)
         {
 
             SpawnOrcTank(_wave.enemyTank);
 
             yield return new WaitForSeconds(0.5f / _wave.rate);
 
         }
 
         tankOrcIsSpawning = false;
 
         state = SpawnState.Waiting;
     }