> try to configure Python with ./configure --with-pydebug
I'm installing 3.4.2 with this option right now and I'll reboot and run the script with gdb attached. I might be a few days before I have a result.

> Are you using other external modules which are implemented in C
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.

> Would it be possible to share your source code
I can share it privately, yes, but running it on your machine might be too complicated. Sharing the source code will probably be only useful for you to look at what libraries I am using and how I'm using asyncio.

What I can do is try running it on another machine with another setup. While it is currently running on a physical machine that I set up, I can run it in parallel on a OpenVZ VPS that is installed by the VPS provider, so it should give a completely independent environment. Would that help? If yes, should I also install 3.4.2 from source with --with-pydebug?