Java APM agent can't create JMX metric

Kibana version: 7.5.1

Elasticsearch version: 7.5.1

APM Server version: 7.6.2

APM Agent language and version: java 1.15.0

Browser version: NA

Original install method (e.g. download page, yum, deb, from source, etc.) and version: linux x64 extractable tar

Fresh install or upgraded from other version?
Fresh install

I am instrumenting a custom load application (not spring boot, jboss/tomcat etc).
I've attempted to add in instrumentation packages as well as JMX information:
apmelastic.properties:

capture_jmx_metrics=object_name[java.lang:type=GarbageCollector,name=*] attribute[CollectionCount:metric_name=collection_count] attribute[CollectionTime], object_name[kafka.producer:type=producer-metrics,client-id=AuditLoad] attribute[request-latency-avg] 

Steps to reproduce:

  1. Start elasticsearch, kibana
  2. ./apmserver setup
  3. java -jar app.jar -javaagent $path_to_jar

Provide logs and/or server output (if relevant):

2020-05-12 12:01:15.133 [main] WARN co.elastic.apm.agent.jmx.JmxMetricTracker - Can't create metric 'object_name[kafka.producer:type=producer-metrics,client-id=AuditLoad] attribute[request-latency-avg]' because attribute 'request-latency-avg' could not be found

That's one of the many warnings printed during startup, and I know that the Kafka metrics exist for that name (confirmed with jconsole) - but likely registered lazily.
I'm not getting any transactions in Kibana either, but I wanted to track down the JMX issues first.

We do add listeners so that lazily added MBeans get captured, too. However, when they're not available on startup, you'll see this warning. Do you get any data, for example heap metrics from your application? If not, there might be a connection issue between the agent and APM Server.

The garbage collection count, "collection_count" is making it's way to Elastic in apm indices. So I don't think it's connectivity issues.