I encountered this problem in Form, which is I couldn’t send a data column to the spreadsheet (it made an empty cell) if the column is created by “Lookup” of a relation.
Then I found it works correctly if I use the column as a component.
As a workaround, because I did not make it appear, I made a template of
ID is the column I wanted to send to the spreadsheet. Then I used the template as a component of the form.
I am posting this because I thought a data column alone should be sent to the spreadsheet correctly in the first place.