What do you mean when you say "from the off mode..."? If you're saying that the alarm will not alert you at the designated time while the iPhone is turned off then you're right. It's been like that with all of the previous iOS versions I've used, unless I'm mistaken. If you mean that the alarm will not alert you while the clock app is closed then I disagree because that has not been my experience in iOS 10 or the previous iOS versions.