Typically, when you load a design in Clarity 3D Layout, it might have some potential layout issues causing bad simulation results, or sometimes, the simulation may even fail. You need to rectify the layout before the simulation.
Clarity 3D Layout offers a new option to sanitize your layout before a simulation.
To access this new option, click the Sanitize Layout button from the Object toolbar. You will be presented with the Sanitize Layout window. By default, all options are selected. You can check/uncheck the sanitize options to be run by clicking the checkbox to the left of each of them. After selecting all desired options, click the OK button to apply the changes and update your layout.
Cadence Design Systems
Further you can refer to the following application note on Sanitize layout options in Clarity and Sigrity tools:
Sanitize Layout Option for Clarity and Sigrity Tools