WP7104 NAT iptables

I run modem WP7104 on Linux (kernel 3.12.11). I establish network using qmi and dhclient on wwan0. I retrieved ip adress from local dhcp server.
Now I want to establish LAN network. I used to iptable -t nat to set masquerade wwan <-> lan. On the LAN side I see on tcpdump that TCP connection is establishing and right after that is finished withot reason. Ping to remote hosts over masquarade works fine. Using other modules and same way to set masquerade, it works perfect. Is any setting missing on module side?

I use also dedicated modules GobiSerial & GobiNet ver. S2.19N2.24 but without succes. Still can not receive TCP data packets. ICMP, UDP packets are overtaken between network interfaces using SNAT (iptables). Host & client start his TCP sesion and after send FIN(close sesion) packets.
It seems it a bug in tcp/ip stack in drivers.
However using standard qmi drivers: qmi_wwan & qcserial and cdc_wdm and established connection over PPP protocole works fine, all tcp packets data are transmitted between network interfaces using SNAT (iptables).
Unfortunatly PPP conection is not efficient for 4G (LTE).

we have sierra experts working on this issue. I’ll update you once i get some answers.

Thanks you for your patience.