C7500 Wifi and Admin Issues

ISP: Sparklight (formerly CableOne)

Model: Netgear C7500|Nighthawk X4-AC3200 WiFi Cable Modem Router

Firmware: V1.01.39

OS: Windows 10

I apologize ahead of time for the novel...I'll try to break it up.

tl;dr: Amazon Renewed C7500, started losing wifi connection, then admin pages stopped working properly. Tried factory resetting through GUI and with reset button, only intensified issues. Firmware reflash needed, or defective unit?

-----Start of issues

I recently purchased an 'Amazon Renewed' Netgear C7500 to replace my old modem and router. After I customized the wifi settings (ssid, security key, channels, etc) I noticed that when I was trying to connect to the 2.4ghz network, it would not connect, then my computer wouldn't even see the network until rebooting the modem. This continued so I decided to just disable the 2.4ghz radio as my devices work just fine using the 5ghz, and I get the range/speed I need. So I was content with this setup, but am unsure if this was just the start of my problems.

-----Main issue

Then a couple of days ago my Amazon Fire stick started dropping connections (it may have happened on other devices, but this was the only one being used at the time) so I went to check settings in the admin pages. Only when I login, it takes forever to load, then about 15-20 seconds later it asks for the login again. The frame of the page then loads, but the content for the current tab either stays blank, or I get a browser timeout. I can click on some of the other tabs and after about 20-30 seconds it asks for the login, then after signing in it loads properly. About 50% of the available options both in the basic and advanced settings load

I have tried multiple browsers, first with Opera GX v. 67.0.3575.130, Google Chrome v. 81.0.4044.129 and v. 81.0.4044.138, and Microsoft Edge v. 44.17763.831.0. I have also tried using the Netgear Genie app, but going to any section that requires login (the important ones) either says it can't find a compatible router, or it will let me enter the username and password (saved) and click login, but then just shows the loading wheel with no activity happening after 5+ minutes.

-----Attempted Fixes

I have attemped to return the unit to factory default settings multiple times and ways. Using the admin pages, (one of the pages that I am able to access) it compounded my issues to where half of the admin pages that are working are missing settings. (e.g. advanced -> advanced settings -> wireless settings the 2.4ghz network doesn't have any values for fragmentation length or the cts/rts threshold) I have tried manually entering default values and applying them, only to have the router say its applying changes, reboot, then the page reloads still without any values where I entered them. All previous issues are still present.

Next I used the reset button, with the same results as on the gui.

-----Extra Info

I'm wondering if it could be a corrupted firmware as when I activated the modem the self-activation was seemingly having issues taking a while and rebooting at least 2 times (which I'm guessing now was mostly because the router needed to download the firmware) and said I had to call tech support, so I did and we got it activated after a few more reboots. (the tech was suprised at how many reboots)

-----Solutions?

This product is still under the Amazon Renewed warranty (I also purchased a suggested 4-year extended warranty through them), is this something I should send back? Is it possible the firmware is corrupted? I have read on upgrading the firmware on this unit, and it seems it is tied to the ISP. I have called tech support and they said that because I own the modem they can't do anything except power cycle the modem and to contact Netgear to find out how to upgrade my firmware. I'd really hate to have to return this product and not have internet while waiting for the replacement (as I have school), so is there anything I can do?

edit: For general readability