Are you running the multicurrency version of QBO for yourself or one of your clients? Do you use recurring transactions? If you answered yes to both of those questions, then you need to read this:
When you set up a recurring transaction in a foreign currency, QBO retains the exchange rate from the date you set up it up. The exchange rate is not driven by the new date that the transaction was created.
To populate the correct rate, you need to open the transaction, adjust the date by one day and then move it back to the correct date, and it will grab the correct exchange rate.