When checking Mandatory Pre-fill, located in System Admin-> Configuration -> External Request -> Section A , any option select both Display and Mandatory Prefill for a option like Position Title. When going to the form the position title is not automatically populated with the user's position.
SAP SuccessFactors Learning
Mandatory and Pre-Fill are two seperate Columns though they can look like one at times.
Pre-Fill will only work for those rows that have the Dropdown Menu. Mandatory does not mean it will pre-populate.
KBA , LOD-SF-LMS-EXT , Sites and External Users , Problem