So my previous issue seems to have taken care of itself, I suspect it might have had something to do with improper minimap icons for some custom assets but I'm not sure.
For anyone still interesting in helping me troubleshoot here's one for you:
Player 1 creates a map and runs it through levelpacker.exe. He then hosts a game using said map that Player 2 proceeds to download. The game starts fine, except that there are some elements on Player 1's screen that do not appear on Player 2's screen. When Player 1 interacts with these elements it causes Player 2's game to crash. Note that there are custom assets that appear fine for both players.