Macbook Startup Freeze
This issue first began when I attempted to wake the computer from
  sleep by opening the lid. Instead of the normal login screen,
  everything stayed black.


The Black screen was caused by this error.



It tried to load your Screen lock .png but failed to do so. 

Remove Screen lock settings, reboot and see if it works. Reset Screen lock with new message.

Since the Screen lock settings resides in NVRAM it will remain unchanged even if you upgrade to new OSX or Reset NVRAM.