Things that were broken by the new code added there:

• Passing $fields = 'u.*'. You get debugging like 'Debugging: get_role_users() adding u.lastname, u.firstname, u.id to the query result because they were required by $sort but missing in $fields'
• Passing $fields = 'u.id AS some_alias'.

I am also pretty sure that the call to get_role_users in grade/report/singleview/classes/local/screen/select.php is likely to trigger the new debugging, and needs to be fixed.