Removed speed setting affects SFP+ interfaces after upgrade
Starting in FortiOS 7.6.1, the 1000auto speed setting is removed. If a FortiGate SFP+ port speed is set to 1000auto before upgrade, the upgrade process automatically changes the setting to 10000full. This change can cause the interface to go down when the connecting device has a different speed setting.
Workaround: After upgrade, align the port settings. Edit the port and set the speed to 1000full to restore the connection.
config system interface
edit <port>
set speed 1000full
next
end