There seems to be an embedded NULL character in the column that is being fetched. In R we cannot have embedded NULL. Query the the table for that column and row, and remove the NULL character and try agiain.
R treats NULL characters as the end of a string and anything after it will not be displayed. But Oracle allows embedded NULL. How was this data inserted? You might be able to fix it by either by replacing NULLwith a new line or blank or truncating after the NULL character if the data after NULL character is not needed.