The internet cuts off between 2 AM - 5 AM every night, it's been getting worse.

My internet connection drops around 2 am, then it drops again at 3 (or sometimes at 4 am), and again at 5 am. (+ randomly slows down or cuts off during 2 - 5 am).
It used to be not this bad before but it has been getting so bad recently and becoming very annoying.

I am currently using xFi Wireless Gateway (DPC3941T) and I never had this kind of issue when I used my own modem and router back then.
So I am wondering if this issue may be caused by Xfinity’s gateway somehow.
(I spent hours tinkering with the gateway settings but I couldn't figure it out).

I paid for the full 24hours internet service and it is quite funny that I can't use the internet for 1/8th of 24 hours; I am so frustrated.
Does anyone know how to resolve this issue?