The line sdwan_mbr_seq=1 sdwan_service_id=4 indicates that this session is part of an SD-WAN rule. sdwan_service_id=4 confirms that the session is being handled by SD-WAN rule ID 4. This directly links the flow to the SD-WAN configuration.
The line no_offload_reason: redir-to-ips denied-by-nturbo shows that the session is not offloaded to the NPU (Network Processing Unit) and is being processed by the main CPU. A session that is not offloaded can be re-evaluated. If the outgoing interface (the one currently being used) goes down, the FortiGate will re-evaluate the session against the SD-WAN rules to find a new active member to steer the traffic through. This is a fundamental behavior of SD-WAN, which ensures network resilience.

From the SD-WAN monitor in FortiManager:
"The SD-WAN monitor provides a summary view of the branch devices and their members. In the scenario shown, it is clear that branch2_fgt is missing SLA configuration for one member, as evidenced by the lack of performance metrics. The monitor also shows only two branches in the current topology, allowing quick assessment of branch health and configuration completeness." This kind of visibility is vital for proactive monitoring and rapid troubleshooting in SD-WAN environments.
Reference:
[FCSS_SDW_AR-7.4 1-0.docx Q18]
FortiManager SD-WAN Monitoring Guide, "Branch Device Health and SLA Status Visualization"

The SD-WAN monitor's table view in FortiManager provides a donut visualization plus a detailed table that shows each SD-WAN member's status and SLA pass/miss, giving the per-member health view you're after.

This configuration demonstrates a typical IPsec setup for SD-WAN overlays where the hub side requires a manually defined tunnel IP address, and the spoke can be flexibly configured, including interoperability with third-party IPsec devices. As described in the Fortinet SD-WAN Architect Guide: "For some overlays, the tunnel interface IP is configured statically on the hub side, which allows more control over overlay subnetting and facilitates the use of user-defined overlay IP addresses. This approach is also a requirement for compatibility with non-FortiGate endpoints, such as third-party IPsec devices that may not support dynamic address assignment via IKE or proprietary mechanisms." This enables hybrid SD-WAN environments and advanced designs involving external partners or cloud services. Overlay IP flexibility is critical for route control and segmentation.
Reference:
[FCSS_SDW_AR-7.4 1-0.docx Q11]
FortiOS 7.4 SD-WAN Reference Architecture, "Overlay IP Address Management" SD-WAN 7.4 Concept Guide, Section: "Interoperability with Third-Party Devices"

When an SD-WAN member is deleted, FortiGate can also remove static routes that were tied to that interface. If those routes are needed for destinations not covered by SD-WAN rules, traffic to those networks becomes unreachable. This explains why flows not matching SD-WAN rules are interrupted after the member was removed.