Raspberry Pi Compute Module 4 eMMC flashing issue (nRPI_BOOT)

I recently got my hands on a Raspberry Pi 4 Compute Module, 4 GB with 32 GB eMMC flash and a Compute Module 4 IO board. Due to the global chip shortage it's hard to find one in stock but I got lucky by checking [rpilocator.com] (https://rpilocator.com/) regularly (thanks to [Jeff Geerling] (https://www.jeffgeerling.com/blog/2022/its-dire-raspberry-pi-availability-tracker-launched) for that site. He's got amazing Raspberry Pi related content next to a bunch of high-quality Ansible playbooks, go give him a visit).
The eMMC edition I have can only be flashed if you put a jumper on a pin on the I/O board (to put the cm4 in a special mode, `nRPI_BOOT`) and use a special tool, [usbboot](https://github.com/raspberrypi/usbboot). [Jeff has a great guide](https://web.archive.org/web/20220226203155/https://www.jeffgeerling.com/blog/2020/how-flash-raspberry-pi-os-compute-module-4-emmc-usbboot) on flashing the cm4 eMMC edition. My `cm4` however, was not showing up whenever I put it in this special flashing mode. This article goes over the troubleshooting I did and the eventual solution (hint: hardware problem).