You are probably using the stamina battery saving mode or Extended Standby Mode which prevents Sleep as Android from waking up the device ans so the alarm will not ring if this mode is enabled.
For stamina mode, you can either disable this mode or add Sleep as Android to the active applications in standby. The option resides in settings->Power management. To add Sleep as Android to the active applications in standby, click on “stamina mode”, then “Add applications” and check Sleep as Android.
To disable Extended Standby Mode, go to settings->Power management and then uncheck Extended Standby mode.
Please first check to you have sufficient connectivity, ideally a home WiFi at the time of synchronization. If synchronization is still an issue, please send us a debug report directly from the backup add-on in Settings > Backup > Menu > Send debug.
Noise & Snoring
Please check that you have enabled noise recording in Application settings → Sleep noise recording. Noise recording in not enabled by default as it causes slightly increased battery consumption during sleep tracking.
Huawei together with Xiaomi are the most troubled phones on the market, some vendors tent to ignore Android best practices and implement very bizzare custom modification which make background task nearly impossible to run.
Please take a look at http://sleep.urbandroid.org/documentation/faq/alarms-sleep-tracking-dont-work/
From various error reports we know that the accelerometer sensor implementation on some firmwares has issues. Over the time the accelerometer may get into a broken state and it stops sending data. The only way we know to resolve this issue is to do a reboot. In all cases so far, reboot did solve this issue.
To test whether the accelerometer is working, you can use menu > test sensors or some 3rd party app such as Sensor List.