I'm sorry for posting up new threads. The "black screen of death" problem I created a new thread for here:
https://retropie.org.uk/forum/topic/10640/new-black-screen-of-death

The original error I had, about the invalid pointer, still occurs occasionally. I'm also having a new problem, where upon returning to the menu after playing a game, my D-pad acts like its stuck. I remember this being a problem before because of the raphnet NES adapter. It's weird. My whole system acts like the "update all installed packages" essentially did a format and fresh install.