Answer
Check which underlying dataset/table region the field actually belongs to before assuming the layout is broken — a field can exist in the report's data model but have no data in the table/region you happened to drop it into (for example, being available on a header-level table with no matching XML data, while its real values live in a detail-level table). Check the report's Data XML to see which table actually carries values for that field, then move the field into a region bound to that correct table — it displays correctly once it's referencing the table that actually holds its data.