Discrepancy in Chart of accounts and Trial Balance for a bank account in foreign currency

We have recently closed a bank account in a foreign currency; the Bank reconciliation (which is in the non-sterling amount) always balanced, and Chart of accounts showed nil balance in the account (in the non-sterling currency) on the date the account was closed / date of last transaction. Then my accountant, noticed a remaining GBP balance in this account but in Trial Balance. I have meticulously been posting each transaction in this foreign currency bank account to correspond to the correct FX daily rate in the home currency (based on our bank rates and not Quickbook rates) so I do not understand why there is a remaining GBP ££ value in this account in Trial Balance, when Chart of Accounts showing nil $$. The accountant posted a journal to clear the GBP amount from the Trial Balance (since the account is empty and now closed) but now this GBP amount is in Chart of accounts, which is no longer nil $$.

Anyone has any explanation what may have happened there? Where does the difference comes from when workinig with non-home currency bank accounts (USD, EUR etc): you can see a well balanced account in non-GBP currency in Chart of Accounts (correct per Bank statements)  and then Trial Balance showing an incorrect amount in GBP?