My property buyer/s pulls out of the Agreement of Sale and completion of contracts due to my failure to disclose material information affecting the condition or value of my property?

You will not be able to trigger ClozeSure.

This is a breach of contract due to your failure to disclose material information affecting the property.  You will almost certainly be liable to return the deposit to the buyer (who may bring a claim against you for the costs, damages and losses they have incurred due to your breach of contract).  ClozeSure cannot be triggered by a seller who is in breach of their sale contract or who has provided false or misleading information in pre-contract enquiries.

Note that you will not be entitled to a refund of the ClozeSure fee.