Filters that are derived from the custom user fields are missing in the user search on the People page. This blocks the users from filtering the search results but these filters.
This issue was identified as a bug and resolved in Jive Cloud release 3006.8 with the issue key JVCLD-105304 (release notes on Worx). While the Cloud upgrades are automatically deployed, if you haven't yet been upgraded or have chosen to stay on an earlier version and now would like to upgrade, please get in touch with your Account Manager/Executive to arrange for the upgrade.
After the upgrade, you will be able to use the custom user fields as filters in the user search on the People page.