@AdamLaFever-5575 Is it possible that the client cert is being used or referenced within multiple places?
The next item we would like to have you check is to go into the Azure portal and navigate to your App Registration. Can you verify that the App Registration is indeed active and not expired? Ensure it matches the one being used in your pipeline.
Third item to check is any environment variables that you might call on the web app. Please ensure that any variables in place related to your client secrets have been updated. This one is more hidden on the configuration blade of your Web App and is often missed by many.
The final items that I can think of would be around permissions. Can you verify that the App Registration has the necessary API permissions, that your service principal associated with the App Registration has the correct role assignments and lastly ensure there are no conditional access policies in Entra ID that could be affecting the authentication flow.