session expired suddenly after just receive 'Unable to read data from server'

The below is what i received at zookeeper client. Something i can't
understand is time between 'unable to read' and 'socket connection'. As you
see at below, that is just 1 second. That is too small for expiration.
negotiated time of the client is 6000ms and tick time is 2000ms. In my
opinion, it should be at least 4 or 6 seconds to get expiration from
getting 'unable to read'.

What i'm currently suspicious about is JVM setting. Before I set up
concurrent garbage collector on zookeeper server, there were really many
connection loss. Can that weird connection loss come from not setting up
garbage collector on zk client JVM? There were no gc logging at the client,
and i can't reproduce this error.

thanks for reading.