If every transaction in the bank account is reconciled, and the sum of these matches the reconciled balance, then the difference will be due to the transactions in the data. In the first instance, please check the following:
The original Opening Balance import matched the opening balance of the first statement to be reconciled
All transactions in the data are matched to a statement rather than having been reconciled manually.
For further assistance, our support team will need to investigate, run scripts or liaise with the hosting or development teams. Any Issues with contacting us, please see the following Get support in Access Financials.