Why is Linux monitoring agent not available in dashboard to add to APM 8.1.3 application?

We have APM 8.1.3 monitoring agent for Linux OS running on Red Hat Enterprise Linux Server release 7.3. It is running and shows as online in APM Dashboard under Advanced->Agent Configuration->Linux OS.
![alt text][1]
However, when we try to add Linux OS component to an Application in dashboard, the agent does not show up, and cannot be added to the application. What could be causing this issue?
![alt text][2]

[1]: /answers/storage/temp/12232-agentconfiguration.jpg
[2]: /answers/storage/temp/12233-linuxos-missing.jpg