To track outstanding Client Tasks, we recommend adding a Tasklist Automator to the section of Client Tasks. You can set this Automator to move the work status to Waiting for client, or another custom status that will help you understand that you are waiting action from your client.

When you filter your work by the status Waiting for client, you'll be able to see a full list of work items where you are waiting for client action.

Additionally, you could turn on the Global Automator to update the status of work to a custom status like Resend Client Tasks when all 5 client task reminders have been sent and the Client Tasks are incomplete.