Have you accounted for prepayments? Anything where you’ve paid a supplier or been paid by a customer but not yet received/sent the invoice will count on the relevant control account but not in the sales/purchases total.
The other possibility is to check the date ranges match, the balance sheet shows an all-time figure but you may be looking at invoices just in a certain period so you’d need to adjust for any opening balance on the control accounts at the start of that period.