@T-thorel Ok you passed the dhcp issue and pxe boot issue. Now the issue is with the iPXE program that creates the FOG iPXE menu.
Typically when we see this error it is because your building network switch is using Spanning Tree protocol but not one of the fast spanning tree protocols. A test for this can be to find a dumb/cheap/unmanaged switch and place it between the pxe booting computer and then building network switch. If the computer pxe boots correctly into the FOG iPXE menu then you will need to get with your networking/infrastructure group and have them enable one of the fast spanning tree protocols like portfast, RSTP, MSTP, fastSTP, or what ever your switch manufacturer calls it. This setting will need to be enabled on every user facing port where you need to pxe boot.
The issue is that FOG boots too fast. It will give up trying before spanning tree starts forwarding data on the network interface (~27 seconds after the link light is turned on).