Hi,
A means Assembly. Your database is inconsitent.
Work around recommendation:
Go to BOM and create a BOM for this item, then remove that BOM and execute query to see if treetype back to "N" value or not.
If "yes", try to open a new marketing document and check to see if item description appears or not.
If "no", raise a ticket for SAP support.
Hope this helps,
TVSon