Please check if the problem is appearing in the latest firmware version WW-16.2017.2004.063.
If there are battery drain issues in sleep mode, please kindly follow the steps below and show us the screenshots.
1) Charge the phone to 100% before going to bed > remove the charger > Clear all apps in recent app list > turn off screen > the next morning before using the phone, please screenshot the two pages:
a) Settings > Battery
b) Settings > Battery > ""Advanced battery usage"" (tap the battery icon to access)
Thank you 🙂