If you want to be sure that your cluster is in excellent health, sometimes perform these checks on each cluster member via console:
conf glo get system status get system perf status diag hardware deviceinfo nic [Port_n] diagnose debug crashlog read diag sys session stat diag sys ha checksum cluster diag sys ha dump-by vcluster get sys ha status show system ha
On the output is easy to find the health state of the sync!
You can also monitor the sync status by configure HA email alert on: Log&Report > Email Alert Settings > Administrative > HA status change (on)
In this way you can view in real-time the syncronization status of the Global/Vdom Fortigate.