I was asked to create a separate thread about my case. As a recap, I will paste the comments that I left in the other thread: https://community.tp-link.com/en/home/forum/topic/219606?page=1

Model: Deco X20

Hardware Version: V1.26 (it says US/1.26 on the bottom)

Firmware Version: 1.5.1 Build 20210204 Rel. 50738

I have similar issues where my Deco router crashes (sometimes multiple times in a row) and the lights underneath the Deco is red. All my devices are still connected to the router, but the router isn't giving an internet connection. I have it connected to my ISP's router and its operation mode is Router. The connection on my ISP router is very stable. I was convinced that the Deco crashes because of my Dell XPS 9360 laptop (everytime I turn on the computer, the router crashes). However, the Deco router crashed several times without my laptop on. I have reboot it several times, I tried resetting it, I changed the Decos around (I have two of them), I have turned off beamforming and guest networks, but left 2.4GHz band on as my camera system needs the 2.4GHz.

Is there anything else I should try? I bought these routers 3 months ago and the problem recently started two weeks ago.

1. My ISP is Optimum (or Altice). The model number of the modem is: UBC1326. Its a router and modem combination. 

2. Yes, rebooting the main Deco does help. Sometimes it solves the issue for a few hours; most of the time, it fixes the issue for a few days.

I installed the beta firmware for a few weeks now. The internet on my Deco X20 still goes down and the led turns red, but not as often (internet drops maybe once or twice a week and a reboot fixes it). I also noticed an interesting scenario. When the internet crashes, any phone or computer loses internet connection. But, devices like my firestick and ring camera system still works. It is still connected to the internet even when the Deco has no internet. If I check my Ring app when the internet goes down, I am able to view the video on all my ring devices, even if I disable WiFi on my phone. And my firestick continues to stream even when there is no internet connection. Is there any reason that can cause this to happen?