It looks like you are using ISPN 5. Can't you update to the most recent version (currently 7)?
Anyway, it looks like some nodes are leaving the cluster. This can happens if you have long GC pauses and the node stops responding to the heartbeats. You can try to tune the GC and/or increment the timeout in FD* protocols in your JGroups configuration.
Thanks for replying.
If the GC pause is too long, after the GC the system should be back to normal.
But the issue occurs for hours together when we try to add to cache.
The issue is not resolved unless one server is restarted.
I just wanted to confirm if this a bug in ISPN 5.