Keep doing TCP Retransmission with ACK, PSH

Hello everyone, here is my situation: I got two servers, a loadbalancer (prowered by softlayer) and a web server running apache 2.2 and php 5.4. My web application only serve android mobile device. I was tested 2 set of server setting: Setting A: traffic directly point to web server Setting B: web server as a node of the loadbalancer, and traffic is pointed to the loadbalancer

For Setting A, everything seems alright, packet have not lost and 3 way hand shark and connection close is done properly. However, for setting B, connection seems unstable, some request have [TCP Retransmission] with ACK + PSH flag. After 4-5 time TCP Retransmision (average took 40 second), the connection establish and data are sent.

What possible makes the client keep sending ACK + PSH? Please help.