> The only module that I'm using that's implemented in C is ujson https://pypi.python.org/pypi/ujson . If you think this is relevant, I can easily try changing it to use the built-in json.

To investigate an issue, we have to reduce the scope. If your program works with json, please use it instead yes. If the program still crash with the builtin json, it means that usjon is not the problem. If the program doesn't crash anymore, your issue may come from ujson and the investigate would be completly different...