We have a custom transaction line field in the Sales Order. It is automatically copied to the Item Fulfillment and to the Revenue Arrangement (native functionality). But, it does not appear in the Revenue Recognition JE anymore. What could be the reason?

Does it show in journal form at all? Is the RevRec journal summary or detail? Is there any value in the field and is not pulled through?

Yes, the field is showing in the JE form. There is a value carried over until Revenue Arrangement. The Rev Rec JE is detailed.