Port forwarding gateways are deprecated as of SynergyCP 5.0 and will be removed in a future version. Switching to the IP-to-IP forwarding gateway is recommended.
The forwarding gateway’s internet IP must be the first IP listed on your NICs, and the local IP must be the second IP on your NICs.
Ensure that the BMC has IPMI over LAN enabled. Most Dell/HP systems do not by default, instead they only enable their proprietary, non-IPMI protocols. You can usually enable IPMI over LAN via the iDRAC/iLO control panel.
Make sure that the gateway is able to connect to the IPMI device, SSH into the gateway and run this command, replacing the variables in single quotes with your information:
apt-get install -y ipmitool
ipmitool -H '<ip>' -U '<admin_user>' -P '<admin_pass>' -I lanplus chassis power status
Try updating to the latest version of the gateway using the install script on the forwarding gateway page, then pasting the new API key into the edit page for the gateway.
Try switching the gateway between IP to IP and Port to Port.
Try disabling port forwarding on the server having issues, then re-enabling port forwarding via the Server Edit page.