for Excel DI uses ADO Inteface provided by Microsoft, the column data is numeric so its returned as Decimal. The ADO interface automatically detects the datatype of the column based on the data in the cell for first few rows (8 - 10)
its hard to tell from the screen dump what might be causing the issue, can you attch the excel sheet by reproducing the issue with few rows
have to tried by removing all the formatting for that column ?
the columns that are displayed or read as NULL in DI have errors in the excel sheet, the ADO interface will return NULL for such cells in the excel sheet
you will have to fix the error for the cell before loading data to DI, check the source of excel that is adding data to the excel