After upgrading to 8.4.1, CAC authentication fails. After clicking the Certificate button, the screen just flashes and then the login prompt reappears. After logging in a second time, an "Internal Error" appears on the login page.
This is caused by a limitation in the 8.4.1.56979 build with users with uppercase characters in their CAC ID.
This has been resolved in Security Analytics version 8.4.1.56980, which is the latest release currently available on the support download site as well as through the upgrade server.