Amazfit Cor automatically detect your sleep, meaning you just need to wear your watch to bed. After you sync your watch in the morning you'll see your sleep information (including light sleep, deep sleep, when you awake, when you asleep etc.) from the watch and Amazfit app.
It analyzes the time you woke up based on the status of your wrist and body, If you woke up but in a completely still state, the device may judge that you are being sleep. However, if you turned over during sleep, the device may judge that you are awake.
May I ask what times were you expecting to see? Or, what times did you sleep that did not show up? Did you wear the device when you were sleeping?
Currently, the watch can record the sleep from 6:00 pm (the day before) - 10:00 am. If you are sleeping during the day or sleeping outside of a typical sleep hour range, the watch will not record or display your sleep. We suggest you keep using your watch. If you still find that the sleep data not accurate, please let us know and illustrate the specific situation ( like when you wake up during the night).
And also please submit a feedback on Amazfit open APP>>Profile>>Feedback), and also send your Amazfit ID (APP--Profile--ID) here so that our tech support can locate your issue and find solution.