Fix your SharePoint 2016 Search after installing KB4462155
If you install the Security Update for Microsoft SharePoint Enterprise Server 2016 (KB4462155) Search may break. This typically happens when you have crawl rule that crawls both:
  1. http://<sharepoint_portal_url>
  2. https://<sharepoint_portal_url>
One possible workaround is to configure your crawl rule to only search https://<sharepoint_portal_url> as the Search Content Source. Of course, this will fix search when you access the portal with https, but not http.

Fortunately, Microsoft released a fix for this issue on 2/27/2019 which is available at

To install the patch:
  1. Download and install the Update.
  2. Restart the front-end SharePoint Server. A reboot of the back-end SQL Server is NOT necessary.
  3. Start Central Admin.
    1. Click on Manage service applications, Search service application.
    2. Click on Content Sources.
    3. In the Local SharePoint sites drop down list box, click Edit
    4. In the Start Addresses verify you have the correct address. Usually this is http://<sharepoint_portal_url>. Only the http entry is necessary, https://<sharepoint_portal_url> is NOT necessary.
  4. Reset Index and Full Crawl.
  5. Verify search is working for http and https

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