Most likely, your server is taking too long to respond and the client is getting bored and closing the connection.
A bit more explanation: tomcat receives a request on a connection and tries to fulfill it. Imagine this takes 3mins, now, if the client has a timeout of say 2mins, it will close the connection and when tomcat finally comes back to try to write the response, the connection is closed and it throws an org.apache.catalina.connector.ClientAbortException.