According to FortiOS 7.6 High Availability documentation, the FortiGate Cluster Protocol (FGCP) provides robust mechanisms for both link monitoring and stateful data synchronization. Link failover is a primary trigger for cluster renegotiation; if a monitored interface goes down-including when an administrator manually sets the interface to administratively down-the primary unit's priority is effectively reduced, triggering a failover to a secondary unit to ensure path continuity.5 This is a standard method for testing HA failover behavior.
Furthermore, to achieve a seamless stateful failover where active sessions are not dropped, the FortiGate performs incremental synchronization of critical runtime data.6 This specifically includes Forwarding Information Base (FIB) entries, which represent the compiled routing table, and IPsec Security Associations (SAs).7 By synchronizing IPsec SAs, the secondary unit 8can resume encrypted tunnels immediately after a failover without requiring a f9ull IKE re-negotiation.10 Statement A is incorrect because in-band and out-of-band management can coexist using reserved management interfaces and management-ip settings.11 Statement C is incorrect because while heartbeat interfaces use link-local IPs in the 169.254.0.x range, the specific IP .2 is not universally required for all heartbeats and depends on the number of cluster members and serial numbers.

From the current HA status, HQ-NGFW-1 is the primary and HQ-NGFW-2 is the secondary.
The administrator then changes these HA parameters:
HQ-NGFW-1: set override disable, set priority 90
HQ-NGFW-2: set override enable, set priority 110
In FGCP (A-P mode), the override (preemption) feature controls whether a higher-priority unit is allowed to take over the primary role.
When override is enabled, the cluster will prefer (and can re-elect) the unit with the highest device priority to become primary (preempting a lower-priority primary when conditions trigger re-election behavior as defined by FGCP).
Here, HQ-NGFW-2 has:
override enabled
higher priority (110) than HQ-NGFW-1 (90)
Therefore, the expected result is that HQ-NGFW-2 becomes the primary.
Why the other options are incorrect:
B is incorrect because it claims HQ-NGFW-2 has lower priority (it is higher: 110 > 90).
C is incorrect because a mismatch in the override setting is not what causes the "configuration out of sync" condition shown in get system ha status (that is about synchronized configuration databases, not a requirement that override values must match to remain in-sync).
D is incorrect because HA settings like override/priority are not synchronized in the way regular configuration objects are; they are device-level HA parameters.

NetAPI: Polls temporary sessions created on the DC when a user logs on or logs off and calls the NetSessionEnum function on Windows. It's faster than the WinSec and WMI methods; however, it can miss some logon events if a DC is under heavy system load. This is because sessions can be quickly created and purged form RAM, before the agent has a chance to poll and notify FG.

Based on the exhibit and FortiOS 7.6 Active Authentication (captive portal) behavior, the most likely reason the user is not presented with a login prompt is that DNS is missing from the firewall policy.
What the exhibit shows
The firewall policy configured for active authentication includes:
Source: HQ_SUBNET and Remote-users
Destination: all
Services:
HTTP
HTTPS
ALL_ICMP
Security Profiles: Web filter and SSL inspection enabled
Authentication: Active (user group referenced)
DNS is not included as a service in the policy.
Why DNS is required for active authentication
In FortiOS 7.6, active authentication (captive portal) works as follows:
The user attempts to access a website using a URL (for example, www.example.com).
The client must first perform a DNS lookup to resolve the domain name.
FortiGate intercepts the initial HTTP/HTTPS request and redirects the user to the authentication portal.
If DNS traffic is blocked or not allowed:
The hostname cannot be resolved.
The HTTP/HTTPS request never properly occurs.
FortiGate has nothing to intercept, so the login prompt is never triggered.
This is explicitly documented in the FortiOS 7.6 Authentication and Captive Portal requirements, which state that DNS must be permitted for captive portal-based authentication to function correctly.
Why the other options are incorrect
A . No matching user account exists for this user
Incorrect.
If the user account did not exist, the login page would still appear, but authentication would fail after credentials are entered.
B . The Remote-users group must be set up correctly in the FSSO configuration Incorrect.
This policy is using active authentication, not FSSO.
FSSO configuration is irrelevant for active authentication login prompts.
C . The Remote-users group is not added to the Destination
Incorrect.
User groups are applied in the Source field for authentication-based policies.
Destination does not accept user groups.

According to the FortiOS 7.6 Administrator Guide and the specific behavior of the SD-WAN GUI, here is the technical breakdown:
SD-WAN Zone Hierarchy and UI Elements: In the FortiGate GUI, SD-WAN zones that contain member interfaces are displayed with a plus (+) icon next to the checkbox. This icon allows administrators to expand the zone and view the specific physical or logical interfaces assigned to it.
Analysis of the "Underlay" Zone: In the provided exhibit, the virtual-wan-link and overlay zones both feature the plus (+) expansion icon, indicating they have active members. The Underlay zone, however, lacks this icon and displays a red status icon. This is the visual indicator in FortiOS that the zone is currently empty and contains no member interfaces.
Mandatory Zone Membership: In FortiOS 7.x, every SD-WAN member interface must be assigned to a zone. It is not possible for an interface to be an "SD-WAN member" (as shown in the legend with port2 and port3) without being assigned to a zone. Since port2 and port3 are listed in the legend, they are indeed assigned to one of the other expanded zones (likely virtual-wan-link or overlay), making Option D incorrect.
Default Zone Behavior: While FortiOS 7.6 often creates default zones like virtual-wan-link, underlay, and overlay during certain configuration wizards or by default in newer versions, they are distinct entities. There is no single "default" zone that acts as a global catch-all in the way Option C suggests.
Immutability of System Zones: While certain system-defined zones have restrictions, the primary focus of this specific exhibit is the current membership state, which clearly shows the Underlay zone is empty.