There is something to the calcium deficiency issue, though - at least 40 ppm is suggested, IIRC. But yeast is my first thought. And if you added CaCl and or gypsum, you should readily reach that level. Lastly, pH should be a bit lower - between 5.2 and 5.4, preferred. Those clean lagers are just not forgiving at anything other than optimal levels for just about everything. But I like them.