No session matched

Hi, guys,

I am using Fortigate 400E with FortiOS v6.4.2, the VIP configuration ( VIP portforwarding + NAT enabled ); 

And I found the "no session matched" eventlog as below:

session captured ( public IPs are modified):

id=20085 trace_id=41913 func=print_pkt_detail line=5639 msg="vd-root:0 received a packet(proto=6, 100.100.100.154:45742->111.111.111.248:18889) from port2. flag [F.], seq 3948000680, ack 1192683525, win 229"
id=20085 trace_id=41913 func=resolve_ip_tuple_fast line=5720 msg="Find an existing session, id-5e847d65, original direction"
id=20085 trace_id=41913 func=ipv4_fast_cb line=53 msg="enter fast path"
id=20085 trace_id=41913 func=ip_session_run_all_tuple line=6922 msg="DNAT 111.111.111.248:18889->10.16.6.35:18889"
id=20085 trace_id=41913 func=ip_session_run_all_tuple line=6910 msg="SNAT 100.100.100.154->10.16.6.254:45742"
id=20085 trace_id=41914 func=print_pkt_detail line=5639 msg="vd-root:0 received a packet(proto=6, 10.16.6.35:18889->10.16.6.254:45742) from Server_V166. flag [F.], seq 1192683525, ack 3948000681, win 453"
id=20085 trace_id=41914 func=resolve_ip_tuple_fast line=5720 msg="Find an existing session, id-5e847d65, reply direction"
id=20085 trace_id=41914 func=ipv4_fast_cb line=53 msg="enter fast path"
id=20085 trace_id=41914 func=ip_session_run_all_tuple line=6922 msg="DNAT 10.16.6.254:45742->100.100.100.154:45742"
id=20085 trace_id=41914 func=ip_session_run_all_tuple line=6910 msg="SNAT 10.16.6.35->111.111.111.248:18889"

id=20085 trace_id=41915 func=print_pkt_detail line=5639 msg="vd-root:0 received a packet(proto=6, 100.100.100.154:38914->111.111.111.248:18889) from port2. flag [.], seq 3102714127, ack 2930562475, win 296"
id=20085 trace_id=41915 func=vf_ip_route_input_common line=2598 msg="find a route: flag=80000000 gw-111.111.111.248 via root"
id=20085 trace_id=41915 func=ip_session_core_in line=6296 msg="no session matched"

id=20085 trace_id=41916 func=print_pkt_detail line=5639 msg="vd-root:0 received a packet(proto=6, 100.100.100.154:38354->111.111.111.248:18889) from port2. flag [.], seq 829094266, ack 2501027776, win 229"
id=20085 trace_id=41916 func=vf_ip_route_input_common line=2598 msg="find a route: flag=80000000 gw-111.111.111.248 via root"
id=20085 trace_id=41916 func=ip_session_core_in line=6296 msg="no session matched"

The above "no session matched" does not like this article ( not match VIP policy):

Technical Tip: Troubleshooting VIP (port forwardin... - Fortinet Community

But the issue is similar to this article:

Technical Tip: Return traffic for IPSec VPN tunnel... - Fortinet Community

Any root cause of this issue ? any recommendation to fix it ?

Many thanks

Benson

Due to three WAN links are formed SDWAN link, is the issue as the following article mentioned:

Solved: Re: fortigate 100E sd-wan problem - Fortinet Community

Thx