Scala Stream Collector on GCP - Not Working

I have been following this tutorial to get Scala Stram Collector running on GCP:

I tried to run the stream collector both locally and on a compute instance but in both cases nothing seems to be pushed to PubSub.

The js tracker seems to successfully find the connection on the ip:port and the streaming collector signals this with “new connection accepted”.

It also appears there is some communication between pubsub and the pubsub topic because if I use a none existing topic then the server fails to load.

However, no events are being streamed to pubsub and after a minute the server logs indicate that the connection had been closed:
[DEBUG] [10/27/2018 10:13:26.098] [] [akka://scala-stream-collector/user/StreamSupervisor-0/flow-5-0-unknown-operation] Aborting tcp connection to / because of upstream failure: HTTP idle-timeout encountered, no bytes passed in the last 1 minute. This is configurable by akka.http.[server|client].idle-timeout.

Any suggestions?

Opened a bug on github for this: