Upgrade fortiweb 3000 E

Hello everyone,
Recently I upgraded my Fortiweb-3000E from version 6.0.2 to the latest version. All my configuration has been migrated to the new version, But my device didn't work and didn't pass any traffic at all. Because I've had a short time, I couldn't troubleshoot properly. So, I had to downgrade to the 6.0.2 version after the downgrade device worked properly.
I can't find the exact information about my problem, because of I use the device in production environment I don't have a second fail chance.
If anyone has exact information about my problem or misconfiguration let me know how can I manage the upgrading operation.
Thank you in advance