Have you ever had your kombucha not turn sour? It is growing multiple skobies over 2 months, has stringy things and no mold, but just tastes like dilute sweet tea. Hmmmm. Any ideas?
I've never tasted Kombucha Tea that was sour. I guess a lot would depend on what kind of tea you use but the sugar you put in the tea gives it a weak sweet flavor. I've always used black tea and it always had a weak apple juice taste to me.
It seems to me that you are doing everything right and I really wouldn't worry about it as long as you let it ferment as long as the recipe requires.