As Chipotle Mexican Grill (NYSE: CMG) tries to bounce back from its damaging food-safety crisis, the company sees online ordering as a huge potential growth driver.However, customers don't like the most recent version of Chipotle's mobile app whatsoever. Furthermore, the company's mobile order and pickup system doesn't work nearly as well in practice as it does in theory.In the past, one of Chipotle's biggest challenges has been keeping "throughput" high during peak hours.