For symmetric encryption, ENCRYPT has members with shared state: secret key, version and ciphers. In order for to provide consistent state between different threads accessing these members, they should be synchronized.

I have implemented one solution by wrapping the state in separate object which can be found here:
https://github.com/tepitebson/JGroups/tree/ENCRYPT_Thread_safety

I also have replaced the WeakHashMap holding the previous keys with Cache in google's guava library so my solution probably is not suitable for an official solution.