It is a bug in ExTwitter. The stream is discarding messages from the process inbox, which is a big no-no. This means that the subscriptions for the second and third stages are never consumed:
https://github.com/parroty/extwitter/blob/master/lib/extwitter/api/streaming.ex#L110-L111
ExTwitter should use a reference and make sure it only consumes messages it knows about. This must be reported as a bug.
Ideally ExTwitter would provide a GenStage producer, to avoid hijacking the process inbox, which won’t work with a GenStage since both GenStage and ExTwitter are trying to use the same process inbox. You can check the issues tracker so see if someone already requested this feature.
