Make sure your watch is tight enough, but not too tight and not too loose.
When you wake up, please make sure your smartphone has the Bluetooth ON, and login to the App. Then, make sure you refresh the App so that it gets all of the new information from your sleep.
Select in the "Home" where it says "Sleep" and you will be able to see all of the details.
Do you usually sleep for 3 hours or more? Or less than 3 hours?
Your sleep during the night that lasts more than 3 hours no matter if it's deep sleep or light sleep it will track. Sleep will be tracked around the clock. However, your sleep will be recorded only if it lasts for three hours (there are three stages of sleep: deep sleep, light sleep and Awake hour).
Going back to sleep after getting out of bed, sleeping in, or playing with your mobile phone in bed will affect the recording of your sleep. Also, if you don't wear the device before going to bed, or if you take off the watch immediately after getting up, the recorded sleep time will be prolonged or inaccurate