Laptop does not hibernate on low battery in sleep mode

I'm running windows 10. In windows 7 on the same laptop, if the battery level reached critical in sleep mode, it would wake up and hibernate itself. Now in windows 10, if it runs out of battery in sleep mode, when I wake it up, it does a clean boot.

My critical battery level is 5% and critical battery action is hibernate. This works properly when the computer is awake.

Update: Interesting! Looking at the system event log on reboot shows a few relevant events during startup:
1) The previous system shutdown at 4:26:23 PM on ‎10/‎2/‎2017 was unexpected.
1) Windows failed to resume from hibernate with error status 0xC0000221.
2) The system watchdog timer was triggered. 3) The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.
4) The system has rebooted without cleanly shutting down first. This error is caused because the system stopped responding and the hardware watchdog triggered a system reset.

A possible explanation would be that Windows 10 consumes more power to hibernate than Windows 7, and a battery level of 5% is not sufficient to allow it to complete the hibernation. This would explain the log entry "The previous system shutdown ... was unexpected", because the system would have stopped due to loss of power, without completing the hibernation and performing a proper shutdown.

You can try raising the critical battery level to, say, 10%, and checking whether you then get the correct behavior.