ISSUEPlesk Migration Manager runs 'tar' under the domain's FTP user. However, if some files in vhost are created by PHP scripts run via mod_php, and if these files have insufficient permissions for FTP user to read them, then these files will not be transferred.
RESOLUTIONA possible workaround is to use the rsync option in Plesk Migration Manager.
NOTE: Umask should be set to 0077 by your PHP scripts.
This problem has been fixed in Parallels Panel 10.4. Consider upgrade Parallels Panel on your server.