There's a gap in the HostController boot sequence between when the external management interface services allow connections and when the ServerInventory service used internally by the HC for managing servers is available. If certain management requests that need to find info about servers come in during this window, an NPE occurs:

[Host Controller] 03:26:38,028 ERROR [org.jboss.as.controller.management-operation] (management-handler-thread - 4) JBAS014612: Operation ("read-attribute") failed - address: ([
[Host Controller] ("host" => "failover-h1"),
[Host Controller] ("server-config" => "failover-one")
[Host Controller] ]): java.lang.NullPointerException
[Host Controller] at org.jboss.as.host.controller.DomainModelControllerService$DelegatingServerInventory.determineServerStatus(DomainModelControllerService.java:788)
[Host Controller] at org.jboss.as.host.controller.operations.ServerStatusHandler.execute(ServerStatusHandler.java:66)
[Host Controller] at org.jboss.as.controller.operations.global.ReadAttributeHandler.doExecuteInternal(ReadAttributeHandler.java:177) [wildfly-controller-8.0.0.Beta2-SNAPSHOT.jar:8.0.0.Beta2-SNAPSHOT]
[Host Controller] at org.jboss.as.controller.operations.global.ReadAttributeHandler.doExecute(ReadAttributeHandler.java:97) [wildfly-controller-8.0.0.Beta2-SNAPSHOT.jar:8.0.0.Beta2-SNAPSHOT]
[Host Controller] at org.jboss.as.controller.operations.global.GlobalOperationHandlers$AbstractMultiTargetHandler.execute(GlobalOperationHandlers.java:151) [wildfly-controller-8.0.0.Beta2-SNAPSHOT.jar:8.0.0.Beta2-SNAPSHOT]

This shows up as fairly frequent failures in org.jboss.as.test.integration.domain.DomainControllerMigrationTestCase.testDCFailover. Any kind of automated tooling that started/reloaded/restarted an HC and then started polling for completion of server launch could hit the same issue.