When there is shadow flickering on the countertop, there are the following 2 reasons:

First: The countertop installation is overlapped. Generating the countertop twice will cause it to turn black. Right-click on the countertop - select Delete;

Second: The cabinet overlap causes it. You can operate according to the following steps;

First step: Right-click on the countertop and select Delete;

Second step: Delete the overlapped cabinet and place it again;

Third step: Right-click on the wall, select Countertop - Countertop Installation;

Fourth step: Select the material and click OK.

Operation completed: