When the checksums are identical, disable override on the primary FortiGate by entering the following command:
config system ha
set override disable
FGCP clusters dynamically respond to network conditions. If you keep override enabled, the same FortiGate always becomes the primary FortiGate. With override enabled; however, the cluster may negotiate more often to keep the same FortiGate as the primary FortiGate, potentially increasing traffic disruptions.
If you disable override it is more likely that the backup FortiGate could become the primary FortiGate. Disabling override is recommended unless its important that the same FortiGate remains the primary FortiGate
To see how enabling override can cause minor traffic disruptions, with override enabled set up a continuous ping through the cluster. Then disconnect power to the backup unit. You will most likely notice a brief disruption in the ping traffic. Try the same thing with override disabled and you shouldn't see this traffic disruption.
With override enabled, the disruption is minor and shouldn't be noticed by most users. For smoother operation, the best practice is to disable override.