On the sn_vul_vulnerability form, the filter_type field is visible only for a fraction of a second when the page loads.
London (after upgrade from previous releases such as Jakarta)
Vulnerabilities (sn_vul_vulnerabilities) is part of a special plugin, Vulnerability Response.
There is a OOB client script that hides this field whenever the value of that field is equal to 'Group Value'. The name of the client script is 'Handle filter type changes'
Note that this particular client script is designed to run onChange and onLoad, despite its official onChange status.
This is default OOB behavior which can be customized to allow the field to be visible under any number of circumstances.
More info on the Vulnerability Response plugin and its applications can be found at https://docs.servicenow.com/csh?topicname=vuln-landing-page.html&version=latest