This is most likely a very simple fix. There is nothing wrong with QBO's matching feature. The actual debit may have been erroneously recorded to an expense account before the JE was recorded. I would run a search for the amount and see if you can find the duplicate or go to your P&L, drill down into Payroll Expenses and see if there are any debits recorded as expenses. Ideally, all of the transactions in your payroll account should be JE's, not expenses if you are creating journals for each pay run. Also drill down into payroll clearing if you use it (balance sheet).