Hi , that is an unusual occurrence. Not confirmed means your PayPal account is not verified. PP confirms addresses by checking the billing address when a credit card is added to an account.
Confirmed should not be the issue. Seller looks at "detail" of your payment page and will show "eligible" for Seller Protection or not. It should show eligible whether your account is verified or not but only seller can confirm that.
Seller's protection is not contingent on a confirmed address as it once was. Some seller may not be aware.