Thank you for the report. This issue was partially solved.
1. download updated module statistics.exe and copy it to folder %plesk_bin%.
Please backup old module before copying.
2. specify registry value SaveFTPLogsDirectory which point where Plesk should store processed FTP log files: [HKLM\SOFTWARE\Plesk\PSA Config\Config]
"SaveFTPLogsDirectory" = "<full destination folder name>"