Delay between two HTTP requests in a common TCP.flow (between 10 - 30 seconds)

After a few more try and some difficulty to read the tcpdump capture from the BigIP, it seems only the response received on the client capture has some delay.

So, on the BigIP and the server, the request and the response are fine, but on the client, i see a delay of 10-30s.

Also, on the bigip, the capture is very difficult to read as some part seems to be missing. On some capture, wireshark doesn't understand or translate the HTTP response (200 OK), but if i look at the multiple TCP packet, i can see the "200 OK" anyway...