Do you get this error just after you make any config change or do any specific action? Have you tried to failover (if you have HA cluster) or reboot the box to see if the message is still present?
I suggest you to open a FortiCare ticket with us so an engineer will be able to investigate it further. A RMA might be needed. Please also log a Putty session, collect the following outputs and attach them to the new created ticket: get system status
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