When following the instructions, after sbt disting and then running Play (in production mode), there were no metrics reported via the Prometheus exporter web page.
Actually there were a few kamon metrics, but not the hundreds of akka metrics I got otherwise when using the SBT Kanela Runner Plugin, in both dev and production mode.
I noticed in the dist-generated start script, there was no -javaagent: JVM argument provided, which I'm guessing is the problem since I understand you're using the aspectj agent to do the instrumentation. Seems the instructions are thus missing the needed step of adding this to build.sbt: javaAgents += "org.aspectj" % "aspectjweaver" % "1.9.6" % "runtime".