Sleep reporting is a little tricky. Different devices collect different types and amounts of sleep data. Different manufacturers then report that data in different ways. It is often the case where your device app may show a different hours of sleep than KrowdFit gets back from their API.
KrowdFit uses what most devices report as minutes asleep, but the device might show you a different number by rounding up, or combining different types of sleep (restless, rem, in bed, etc...) which they may not include in their minutes asleep counter (api).
Additionally some devices allow the user to change the sleep sensitivity setting. When a device is set to a higher sleep sensitivity we find that our data is generally further off than what is displayed in the device app. When sensitive sleep is turned off KrowdFit will generally display a sleep number within 30 minutes of your device app.