WaitForSeconds in Coroutines do not work.

WaitForSeconds seem to not work when the value is over 0, it stops, nothing happens, if the value is 0, it continues, here is a snippet of the code:

 foreach (char letter in dialogue.text)
 {
     dialogueText.text += letter;
     if (skipWaiting) continue;
     yield return new WaitForSeconds(dialogueSpeed);
 }

And here is the whole code in a gist.

Unity Version: 2017.3.1f1

EDIT: Well, WaitForSecondsRealtime works, because i was messing with the Time.timeScale wich affects Time.deltaTime which then affects WaitForSeconds.