Hey there! I'm going to go ahead and answer my question, since I think I found the problem. ***If you want to get straight to the point, it was the HE that was the problem.***
After reading what @ruggb said (and a couple of Google searches), I got the idea to check the Einsy board more, and to test the resistance of the HE as well. Thankfully, I had another Prusa i3 mk3 that I could check against. Nothing was wrong after moving some wires out of the way and checking the board-they both looked the same. I then decided to check the resistance of the HE on each of the printers. This is where I found the problem.
The broken printer's HE read: 0.05 ohms
The good printer's HE fluctuated, but read about: 15 ohms
This was a surprise to me. I triple checked to make sure the variables were all the same. Thermosister plugged in, both been unplugged for a little bit, and haven't printed anything in a day. At this point, I am almost 99% certain that the HE is the problem. I wish I had a broken printer that I could take the HE out of, but I don't.
I'm not entirely sure why the HE broke, but it might have something to do with the heater wires (not thermosisters). They looked close at the heating end, almost touching each other, and could have been shorting out. I ''would'' try to fix it, but I would need more tools, materials, and also confidence that shorting wires were the problem for that.
As for what I'll do, I'm going to try looking for a new HE to replace it with soon. Although if you think it was something ''else'' that's broken, not the HE, please feel free to comment on this answer. ***I will update this answer if and when I replace the broken HE.*** Thank you to everyone who helped me with this problem!
Cheers!