The FTPS server on the remote host falls back to cleartext communication if SSL negotiations fail.
The remote FTPS server running on the remote host is affected by a security bypass vulnerability due to accepting unencrypted commands if SSL negotiations fail. A man-in-the-middle attacker can exploit this to intercept credentials and modify files.
If using Serv-U, upgrade to version 18.104.22.168 or later. Otherwise, contact the vendor for a patch.