Your ISP's DHCP is not functioning properly - ASUS router

I've figure out my own problem now which I'll both share the link to and post below.

Link: https://forums.xfinity.com/t5/Your-Home-Network/How-do-I-get-someone-to-send-a-provisioning-signal-to-my/m-p/3381050 

"What modem do you have? I was finally able to fix my WiFi issue (no thanks to the Comcast techs).

I have the Motorola MB8600 who, up to the point I fixed my issue, I thought worked fine. However, the modem was the source of my issue. The modem has four LAN ports: one accessible to the end user and three under a sticker that could be easily removed. I removed this sticker and connected three devices to it: the Asus RT-AX56U router in LAN 1, an unmanaged switch in LAN 2, and my brother's PC in LAN 3.

I ended up getting an internet connection to my PC (connected through the switch), but all other connected devices failed to do the same. My router indicated that it was a DHCP issue on the ISPs side (see attached picture) and that led me to believe it was the same issue experienced by others on this forum.

I tried many of the solutions provided to me in addition to updating the firmware on my router, but nothing seemed to work. While I was replacing the ethernet cables for the third time in an attempt to find the root of the problem, I decided to reboot the modem with only the Asus router connected to LAN 1. To my surprise, the router started working while all other devices that I connected after the router did not.

The problem ended up being that the modem supported just one LAN connection at a time regardless of what or how many ports were in use. That is how I was able to get an internet connection through LAN 2 for the switch and later for the router on LAN 1. I had assumed that just like my previous modems, this one would support more than one LAN connection because of it having more than one LAN port. It would have been great had the reps informed me of this to begin with so I would not have wasted their and my time.

In sum, my problem was that my modem with four LAN ports could only use one at a time. Instead of following the link in the getting started guide for more details, I assumed it's functionality based on previous experience with other modems. I proceeded to troubleshoot my internet connection woes based on this assumption that Comcast reps did nothing to dispel. They had me trying to contact Asus to reconfigure my router or replace it altogether or have a Comcast technician come take a look at it. They basically tried to sell me a service or have me go somewhere else to get me out of their hair instead of you know, giving me actual service. Although the blame falls squarely on me for holding such a misconceived notion of my modem's functionality, the Comcast reps I spoke to are partly to blame for not having corrected me. Instead of pointing me to different directions and trying to sell me a service, they should have done a proper rundown of my network setup that would have revealed my erroneous belief. Anyway, this has gone on long enough so I hope my failure helps you in finding your solution!

P.S. For those who also own the Motorola MB8600, here's the link that explains why those four ports exist and why you can't use more than one of them simultaneously: https://motorolamentor.zendesk.com/hc/en-us/articles/115010589128-FAQ-The-MB8600-has-four-Ethernet-ports-Can-I-use-these-for-connecting-more-than-one-device- "