Jsessionid creation synchronization/collision problem

[Ramon Pires da Silva]

Currently I am running 6 tomcat instances, each one in a ec2 instance on aws, using the elasticache service, with the following session manager configuration :

 <Manager className="de.javakaffee.web.msm.MemcachedBackupSessionManager"
    memcachedNodes="xxxxxxx"
    sticky="false"
    sessionBackupAsync="true"
    backupThreadCount="3"
    lockingMode="auto"
    memcachedProtocol="binary"
    sessionBackupTimeout="10000"
    operationTimeout="10000"
   />

A few days I had a problem that never happened before, a user accessing other user account, after the login process in the application. I think that may happened because of a jsessionid creation synchronization/collision problem, I know that a jsessionid can't be recreated inside the same tomcat, but different tomcat instances can create, eventually, the same jsessionid. Any help will be appreciated.