Application not available through mod_cluster with errors saying "Can't read host alias"

Issue

• I have several nodes connected to mod_cluster. They're all shown on the manager page, but some nodes are not showing any contexts and applications are not responsive on these nodes through Apache/mod_cluster.
• The JBoss server.log continuously shows messages like the following:

ERROR [org.jboss.modcluster.mcmp.impl.DefaultMCMPHandler] (ContainerBackgroundProcessor[StandardEngine[jboss.web]]) Error [MEM: MEM: Can't read host alias: {4}] sending command ENABLE-APP to proxy 127.0.0.1:6666, configuration will be reset

• Seeing the following error messages repeated:

ERROR [org.jboss.modcluster] (ServerService Thread Pool -- 88) MODCLUSTER000042: Error MEM send
ing ENABLE-APP command to 127.0.0.1:6666, configuration will be reset: MEM: Can't update or insert host alias