a) "Unspecified" occurs when the value for that evar was not sent in the server call or the value persists. Along with visits it is showing the number of visits in which the value was not sent.
b) Sum of line items will not match the overall total given at the top because of deduplication i.e. if the values are sent in the same visit than that visit will be considered as 1 but when you check it in line items than it will be 1 for each value line item. It is not recommended to sum the individual line items and compare with the total.