Your beginning balance will be incorrect if a previously cleared transaction in your register was voided, deleted, or changed, or a new transaction was added and cleared since your last reconciliation.
To resolve this issue, trace the account activity since the last reconciliation until you find the discrepancy. Running these reports can help:
QuickBooks Desktop for Mac 2019 has a Reconciliation Discrepancy Report to help you identify reconciled transactions that were modified, deleted, or voided.
Step 1: Open the Previous Reconciliation Detail reports
Step 2: Identify the transactions that were un-reconciled and manually calculate the difference
If a transaction is modified, it gets un-reconciled. You need to identify these transactions so you can easily calculate the difference on your ending balance and correct it.
The report should help you look for recent transactions that may have been cleared or uncleared unintentionally:
If opening balance is incorrect because previously reconciled transactions were un-reconciled after you converted from QuickBooks for Windows or vice versa, you can do a lump sum reconciliation as a workaround.
If the opening balance has reverted to zero and the file was not sent back and forth between Windows and Mac, you can:
Found a discrepancy?