My home router, running OpenBSD 7.1, won't boot headlessly

Hello everybody,

A couple of months ago, I decided to build my own custom router for my
home network by following this[1] guide. The machine itself works quite
well, except for one glaring flaw: it won't boot up properly unless I
have a monitor plugged into one of the display ports. Of course, this
makes things a bit difficult to debug.

I'm curious if anyone else has encountered such a bug in the past; and
if so, how did you fix it? Below are the relevant specs of my router.

Specs:
- Motherboard: ASUS PRIME H610I-PLUS D4-CSM
- CPU: Intel Celeron ‎G6900
- RAM: Patriot Viper Steel DDR4 2x8G
- SSD: WD Green 240GB
- NIC: Intel I340-T4

Any and all help will be gratly appreciated!

- Zachary

Sources:
[1]: https://openbsdrouterguide.net/