There are several examples of this failing on Travis:

https://travis-ci.org/onefinestay/nameko/builds/15574391
https://travis-ci.org/onefinestay/nameko/builds/15285366
https://travis-ci.org/onefinestay/nameko/builds/14608400
And plenty more.

I can't reproduce it locally, but I suspect it's just that the ``response_greenthread`` isn't being set up in time, so the RPC message gets discarded by the exchange. Hopeful fix here: https://github.com/onefinestay/nameko/pull/95