Hi,
The same problem happens on my website. I delete the file, then file abandonment occurs.
Unknown file in WordPress core: wp-includes/class-wp-http-netfilter.php
Type: File
Filename: wp-includes/class-wp-http-netfilter.php
File Type: Core
Details: This file is in a WordPress core location but is not distributed with this version of WordPress. This scan often includes files left over from a previous WordPress version, but it may also find files added by another plugin, files added by your host, or malicious files added by an attacker.