I am using Xfinity (aka. Comcast). They figured out it's the old cable that caused all these unstable connections. The technician came and replace with new cable. Problem solved and so far so good.

@ArcherC8 Thanks for your reply. Today it happened again at nearly the same time of the day. I tried to check the router log. After rebooting, It only shows the on and off LED log for today...

Recently I encountered the issue of losing Internet connection: the signal light became organe on the router. And I found the model seemed working fine as all the signal lights on it appear normal. I...