Here are some ideas why transactions show up as unmatched in the missing transactions report:

- data is missing (this can happen with manual entries, especially when the transactions look similar)

- the exchange gave the same TX for two deposits or withdrawals thus the software skipped one as a duplicate

- deposits or withdrawals were imported combined (i.e. you withdraw 1 BTC and then 2 BTC, but the deposit is the sum of 3 BTC)

- your deposits are air drops, dividends, bonus, rebates, forks etc and have to be renamed 

- your credit or debit card purchase came in as a deposit, but need to be a trade with the FIAT invested

- your withdrawal is a spend (you sent it off for goods or services) or a Lost (you sent it to a defunct wallet or exchange)