Troubleshooting Tip: How to investigate the error "Federated Upgrade Failed after reaching state downloading"

Solution

When navigating to System -> Firmware & Registration and selecting Fabric Upgrade as highlighted:

The following error may be observed in the logs: A federated upgrade could not be completed by the root FortiGate

• because: version unavailable.
• message: Federated upgrade failed after reaching state downloading.

To diagnose this issue, collect the following logs:

diagnose debug disable
diagnose debug reset
diagnose debug app update -1
diagnose debug console timestamp en 
diagnose debug en

Errors may include:

1. Image Verification Failures.
2. FortiGuard Connection Issues i.e.

To troubleshoot FortiGuard issues, refer to the following: FortiGuard Troubleshooting 

The following screenshot highlights the expected output before the firewall executes the Federated Upgrade:

Workaround: 
Cancel Fabric Upgrade as highlighted in the following article and utilize the standard upgrade option (file upload)
Reference: Standard File Upgrade Guide 

To cancel the federated upgrade using CLI:

execute federated-upgrade cancel