Libra 2 Kobo Libra 2 can not sleep

Hi every one,
I have problem with Libra 2, after reading, I push power button for sleep mode, but sometime my device can not change to sleep mode, can not touch or do anything. I try to hold sleep button and connect device with computer, maybe it will become normal, but contract rise to 100%
I try to factory reset 2 times, also update lasted software version : 4.34.20097 but the problem still happen
How can I fix this problem