As per the known issues list mention in the release of Drupal 8.3.2, certain uploaded files are liable to be deleted in time along with temporary files (default is 6 hours). Files uploaded via webform_protected_downloads (WPD) are susceptible to this unless you set "Delete temporary files after" to "Never" at /admin/config/media/file-system.
I don't fully understand the details of the known issue but I gather that files uploaded via WPD are not recorded in the database as "in use" by a particular entity.
As per the known issues list mention in the release of Drupal 8.3.2, certain uploaded files are liable to be deleted in time along with temporary files (default is 6 hours). Files uploaded via webform_protected_downloads (WPD) are susceptible to this unless you set "Delete temporary files after" to "Never" at /admin/config/media/file-system.
I don't fully understand the details of the known issue but I gather that files uploaded via WPD are not recorded in the database as "in use" by a particular entity.