@Kevin_Z I upgraded the router to a new firmware, 1.3.0 or higher. It seems that the problem resolved. Thank you.

@Kevin_Z Thanks for your quick response. I purchased the router in November, 2020 and a new one came last month. It seems that the reboot problem occurs totally randomly. It sometimes occur...

The router reboots randomly. I have the problem almost everyday. I also checked the scheduled rebooting, but the setting was off. I sent the router to support, but a new one, same model just came....