Meaning: This is normally a positive result and is one of the ad optimization goals, but it’s always good practice to verify this in your DFP.
Step 1: Ask yourself – Is this expected from a recent optimization strategy you deployed?
Step 2: Run your DFP Yield Report and verify if your Unfilled Impressions % has indeed dropped.
Step 3: You should see an improvement in the average ads per page, or IPP (impressions per pageview).
Step 4: Is there a bad ad unit (high unfilled impressions) disabled or removed from the page? If so, then this could be the reason the percentage of your unfilled impressions has improved. Find out by running an Ad Unit report on DFP and pay attention to the volume.
Step 5: Check with your publisher team to see if any changes were implemented.