@JanetS. I hope you're doing well!
Let me help you with this. I suggest you clean the back of your device with cotton and rubbing alcohol and restart it. Turn the heart rate off, save and sync then turn it on save and sync again. Also check these tips to improve the heart rate reading on your device.
Regarding sleep detection, your device will start recording sleep after it detects an hour of inactivity. If you have a light sleep or move too much then this may difficult your sleep detection. Additionally you can try wearing your device on your non dominant hand to decrease the amount of movement it is subjected to. Finally you can restart your device. You can also manually log your sleep time. You can read more about sleep detection here.
Hope this helps.
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