Data- Only Report Export is Missing Off Columns

Hi Guys, 

I'm having a bit of trouble with some columns on a report I'm looking after. 

When I produce the report, all of the information is present and when I export the report to a variety of formats all of the information is present. However, when I export the report to a data- only .xls or .xlsx two columns disappear. 

Has anyone encountered this before or know how to solve it? 

Thanks, 
John