Help: Early 2015 MBP Stuck in Boot Loop

Background Info:

I recently bought a 2015 MBP (16gb RAM) for cheap on eBay.

The ssd wasn't being recognized, but after setting up and 1T external drive, I got it running Maverick. I then used a USB boot of High Sierra using OpenCore. It worked like a charm.

The Problem:

Now, I was trying to update it and it seemed to go through alright. However, I went to boot it up and now it's stuck in a boot loop. Internet Recovery (cmd + r), Safe Mode (shift), and Start Up Manager (option) all don't do anything. I've tried booting it with the external plugged in and removed (to see if it'd give the ssd error again) and it didn't change anything.

I've reset the NVRAM/PRAM as well to no avail.

I can't think of or find anything to get through this. Any ideas? It was only $65 so I'm not super torn if this is done forever, but I do want to get it working.