This can occur when the Splunk Mobile app is installed. Your install is likely ok.
$SPLUNK_HOME/etc/apps/mobile/appserver/modules/account/login.html
This is the culprit. Move this file out to another name, or remove the app and then restart Splunk. Your login screen should appear correctly.
Maybe. This is the first time login page.
What OS? What version did you upgrade from?
This can occur when the Splunk Mobile app is installed. Your install is likely ok.
$SPLUNK_HOME/etc/apps/mobile/appserver/modules/account/login.html
This is the culprit. Move this file out to another name, or remove the app and then restart Splunk. Your login screen should appear correctly.