Check the Cell Level Pin Placement.
1. Whether the Pins in the Cell Level have options for the router to route.
Eg: Output Pin Y, should have at-least 2 or more access point meaning where the Router can place the Via and make the connection)
This should be taken care
2. If the above is not possible, place a FILL cell beside high density cell to borrow a space for the corner pins
Check on EDA site for more information on this.
But for 30% Utilization, You need to take care in Layout Level. Have a look at Cell Level Layout on the Pins where the router is congested.