This page explain the different views showing object complexity in the dashboard
"Complex objects" in the left panel
The line "Complex Objects" in the left panel represents the sum of high and very high Cost Complexity objects in your CAST Environment
"Complex Objects" in Compare version
Added/Deleted H/VH/L/VL Complexity Artifacts in the compare version shows respectively the number of Added/Deleted artifacts with High/VeryHigh/Low/VeryLow between two versions
One cannot directly compare the "Complex Objects" results in left panel and the added/deleted H/VH Complexity Artifacts in Content Evolution when there are updated objects. Indeed, the complexity of the updated objects could changed making them taken into account in complex objects shown in the left panel.
An artifact can be with low complexity in snapshot1 then moves to high complexity in snapshot2. snapshot2 will have 1 more complex objects in the left panel even if this object has not been added (actually, it has been updated)