Spray Client for Jenkins hangs waiting for large response

Question

I'm writing a Spray client for the Jenkins build server. I can query a project with up to 18 build results but a project with 31 has the behaviour that my client never receives the response. I can do this successfully with curl so I'm at a loss for what to look at next.

I do not believe this is about a chunked transfer encoding as I don't see that header in the successful response - although I may be mistaken in my understand of what should happen.

object JenkinsBuildStatus extends App {

  implicit val system = ActorSystem("JenkinsBuildStatus")
  import system.dispatcher // execution context for futures
  val log = Logging(system, getClass)

  val pipeline: HttpRequest => Future[HttpResponse] = (
       addCredentials(BasicHttpCredentials("username","foobar"))
   ~> addHeader("Accept", MediaRanges.`*/*`.value)
   ~> addHeader("User-Agent", "curl/7.37.1")
   ~> logRequest(log)
   ~> sendReceive
   ~> logResponse(log)
)
val response: Future[HttpResponse] = pipeline(Get("https://jenkinsbuilds.corp.com/jenkins/job/Project-Java1.8/api/json/"))

response onComplete {
 case Success(data) => {
   log.info (data.toString())
   shutdown()
 }
 case Failure(error) => {
   log.error(error, "Failure with web client")
   shutdown()
 }
}

 def shutdown(): Unit = {
  IO(Http).ask(Http.CloseAll)(1.second).await
  system.shutdown()
  }
}