When units are out of synchronization in an HA cluster, the GUI will compare the HA checksums and display the tables that caused HA to be out of synchronization. This can be visualized on the HA monitor page and in the HA status widget.
Go to System > HA and hover the cursor over the unsynchronized device. The pop-up shows the tables that caused HA to be out of synchronization, including the checksum values.
Go to Dashboard > Status and in the HA Status widget, hover the cursor over the unsynchronized device (highlighted in red). The pop-up includes the tables that out of synchronization.