I found that use of espconn_tcp_set_max_con_allow(&esp_conn, 1);
when using esp as TCP server in a first period of time will impact establishing connection to the server (running this time as client) in the second period of time.
Now I added in the uninit of my TCP server :
espconn_tcp_set_max_con_allow(&esp_conn, espconn_tcp_get_max_con()); // solve troubles to establish connection as client