Did you verify that this is not related to operating system, network or database issues?
Do you see any messages in the server.log?
I looked at the logs carefully and found one error that was not application related.
ERROR [org.jboss.as.server.deployment.scanner] (DeploymentScanner-threads - 1) JBAS015010: The deployment scanner found a directory named WEB-INF that was not inside a directory whose name ends with .ear, .jar, .rar, .sar or .war. This is likely the result of unzipping an archive directly inside the /usr/share/jboss-as/standalone/deployments directory, which is a user error. The WEB-INF directory will not be scanned for deployments, but it is possible that the scanner mayfind other files from the unzipped archive and attempt to deploy them, leading to errors.
So, initially we deployed all our Apps in exploded format with usual .war folder name.
However, over time, as we performed code changes, we deployed the Apps in the usual .war format (not exploded).
Also, we renamed the exploded .war folder to include .bkp extension (.war.bkp) so that we had an old copy of the code just incase we needed to revert our changes.
I wonder if the above scenario is the main cause of the issue.
It is very difficult to replicate because the issue shows up only after few days on the successful deployment and resolves itself after a JBoss restart.
The issue also seems to be affecting the UI and not the server-side Web Services (which could be related to the above error).
Can the error and symptoms be confirmed?
It is unlikely to be an OS / Network issue (because JBoss Admin Console opens up & App Web Services work fine).