When adding additional profile fields to grade_export_customprofilefields, if the shortname of the profile field contains an uppercase character no data will be displayed in the export but the column heading will still be displayed.

Steps to replicate

• Create a new additional profile field of any kind containing an uppercase character in the shortname
• Add the shortname to grade_export_customprofilefields
• Add data to the additional profile field for a user
• In a course that the user is enrolled in, export the grades
• Additional profile field will display in column heading but no data will be shown

Rerun the test above after changing the shortname of the additional profile field to contain lowercase characters only & edit the shortname in grade_export_customprofilefields.

With debugging turned on I get the following debug output in the exported spreadsheet - 

 Notice: Undefined property: stdClass::$customfield_Abc in /path/to/moodle/grade/lib.php on line 3195