Error: socket hang up

[plowman]

We're running freight + hubot, and a few times a day, Hubot reports the following error trying to speak to the freight web process:

Error: socket hang up

We are using a supervisor to keep freight going, and the run environment looks something like this:

export PATH=~/.virtualenvs/freight/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
export PYTHONPATH=~/.virtualenvs/freight/lib/python2.7/site-packages/
export FREIGHT_CONF=~/freight/freight.conf.py
~/.virtualenvs/freight/bin/python ~/freight/bin/web --addr :5000 --debug

Unfortunately, there is nothing in the logs that's different from when freight is working normally. So far, the only fix we've found is to just restart the freight webserver.

Do you have any thoughts on why this might be happening?