VXrail Nodes cannot reach gateway

I've recently received two new VXRAIL nodes with a witness sled. I've completed the following initial setup steps:

Rack mounted the 2U chassis.
Connected 10GbE network cables from the first two ports of the internal network module on each node to a Fortinet distributed switch, which leads to a Fortinet firewall (network gateway for the ESXi management subnet).
Connected 1GbE iDRAC network cables to both nodes.
Connected the 2x1GbE witness network cables.
Configured iDRAC IP addresses and verified access from a Windows laptop on the user VLAN (with appropriate firewall rules).
Powered on both nodes and the witness sled, confirming successful startup and status via iDRAC.
Accessed the ESXi virtual console and configured management IP addresses for the nodes on the management VLAN.
However, I'm encountering network connectivity issues:

The ESXi management IP addresses are unreachable from the network.
The ESXi nodes cannot ping their own gateway.
Nodes configured on switch-only mode and nodes are not communicating each other
I've thoroughly reviewed the official VXRAIL installation documentation and collaborated with the network team for troubleshooting over the past three days, but the issue persists. 

I've opened a case with Dell support. They've attempted troubleshooting steps such as recreating vSwitch uplinks and restarting the nodes, but the issue persists. While the case remains open, I have limited time for further investigation.

Additionally, someone suggested running the NVTool. However, this tool's functionality is limited until the VXRAIL cluster is configured and VMs are deployed.

Here are some additional details that might help diagnose the problem:

LACP/MC LAG is currently disabled at the switch level due to using standard vSwitches on the ESXi nodes.
I've experimented with configuring a native VLAN on the switch but later changed it back to the default setting.
Could you please review these steps and offer any insights or suggestions for further troubleshooting?