Attempts transactions: These are transactions where the bank is not participating in 3DS but the Visa/MasterCard Attempts Server stands in on behalf of the issuing bank and silently authenticates the cardholder. This will shift the liability off of the merchant and onto the issuing bank.
Unprocessed transactions: These are transactions that did not complete 3D Secure. It could be because the cardholder hit the "back" button during the authentication process (maybe they wanted to add or remove something from their order). It could be because the cardholder decided to abandon the transaction altogether. Or it could be a possible integration issue where the merchant/partner is not performing the bank redirect correctly, which causes the transaction to not complete 3DS.