If you set the reason comment (without a reason code) in a general journal, before setting the offset account, the reason code will disappear.

This should be fixed cause:

The 'Reason comment' field is useful for customer communication. This is included both on letters and in the reason for payment for payments. At the same time, this is an indication for some customers that processing has already taken place. The field is therefore used to provide additional information about the posting.