This article describes how to fix an issue where HA is out of sync and it becomes impossible to manually change the config in both units of the HA setup.
Occasionally, a sync error arises with the system.custom-language object as shown below:
diagnose debug config-error-log read
When this error occurs, a manual change also fails:
config system custom-language
node_check_object fail! for filename
Attribute 'filename' MUST be set.
Command fail. Return code -651
To resolve the issue:
diag sys ha checksum recalculate
If these steps do not resolve the issue, contact Fortinet's TAC team for additional support.