The Unrealized Gain/Loss account is generated after processing Transactions > Financial > Revalue Open Currency Balances. Each month end currency revaluation automatically creates a reversal recorded on the next available period.
As a result, financial report Profit and Loss captures the month end currency revaluation to present the updated values of the foreign account balances. But the reversal of currency revaluation since it is recorded on the next financial period.
While the Chart of Account's Balance column is based on today's date. The account will always show zero due to the reversal entry from revaluation.