Sometimes the AM container for an app isn't able to start the JVM. This can happen if bogus JVM options are given to the AM container ( -Dyarn.app.mapreduce.am.command-opts=-InvalidJvmOption) or when misconfiguring the AM container's environment variables (-Dyarn.app.mapreduce.am.env="JAVA_HOME=/foo/bar/baz)
When the AM container for an app isn't able to start the JVM, the Application page for that application shows N/A for the Started, Node, and Logs columns. It does have links for each app attempt, and if you click on one of them, you go to the Application Attempt page, where you can see all containers with links to their logs and nodes, including the AM container. But none of that shows up for the app attempts on the Application page.
Also, on the Application Attempt page, in the Application Attempt Overview section, the AM Container value is null and the Node value is N/A.