Alright, so I was unable to obtain any sort of logs from the device, unfortunately. But I have noticed something that I didn't before, mostly due to it never having affected any other rom, but when the hybris installation script runs, TWRP outputs a couple lines relating to the data partition not being able to be mounted and its formatting, but the script continues on like nothing's wrong.

Here are the lines in question:

detected filesystem ext4 for /dev/block/platform/msm_sdcc.1/by-name/userdata

mount: failed to mount /dev/block/platform/msm_sdcc.1/by-name/userdata at /data: Device or resource busy

I unmounted the data partition in the mount menu in TWRP, and the error disappeared. But the boot issue still persists. I have also done as you suggested, formatting the data separately from the factory reset, but it hasn't made any difference. I even tried repairing and switching to f2fs and back to ext4, but nothing has helped.

I did indeed do all of those things.

EDIT: The device seems to no longer boot into CM12.1 SFOS at all, I left it for about 8 hours and the only thing that happened was the LED came on. Out of sheer curiosity, I flashed CM13 SFOS over the CM12.1 base and it surprisingly showed more signs of life than the CM12.1 SFOS, in the form of vibrations and the LEDs going on and then dim like on the Ahoy screen and the red shutdown LED.