Hi morta
If previously reconciled transactions have become unreconciled it means they have been changed in some way, this causes them to become unreconciled. In this situation, you would need to undo and re-do the reconciliations. Before undoing any reconciliations I would recommend following the steps under To check where the out of balance occurred in the Help Article Resolving out of balance bank reconciliations.
If the transactions have never been reconciled, they have been entered after the reconciliations were completed. In this situation, you would need to look into those transactions to find out why they were recorded and if they have been posted to the correct bank account.
Recording general journals to reconcile bank accounts is not recommended as this will create further issues.
If you need further assistance feel free to send me screenshots by private message.