I actually did not have the "x number of weapons" quest in my campaign, however the crashes have since stopped occuring. After a few days of doing nothing but running around I was able to access my inventory again without issue.
The game crashes precisely upon clicking "Done" in my inventory, or through a trade window. Edit: Upon further investigation the game crashes whilst trying to leave the inventory screen regardless of what option I click, including trying to exit through the escape key.
I have tried tried...