Elastic agent hangs waiting for first communication with main Bamboo server

Bamboo 2.4 running from its default image which has Elastic Agent 2.4 inside hangs 2 out of 10 times on agent <-> main server communication. What's weird it's not listed on instance list! (https://bamboo.openx.org/admin/elastic/manageElasticInstances.action) The only way I was able to find it was Amazon's console.

The only message in agent's logs is:

0 [main] INFO com.atlassian.bamboo.agent.elastic.client.ElasticAgentBootstrap  - Using tunnnelling. Registering 'httpt' and 'httpst' protocols.
1321 [com.sun.sungrid.service.tunnel.server.TunnelServer] INFO com.sun.sungrid.service.tunnel.server.TunnelServer  - Waiting for tunnel connection.

The Agent (Java process) is working, and so is the monitor in cron, but the instance is not shut down in this scenario and if not finally found (via Bamboo's UI) - it would had to be paid for, but not used.