A system has been configured such that users land on the Modern UX. However, it is noticed that instead of showing the Home tab of the Modern UX, it automatically gets redirected to the Classic UI. The URL being used is of the form https://someServer/pm/#/login. It gets redirected to https://someServer/niku/nu#action:homeActionId automatically.
Release : 16.1.1
In the Classic UI, navigate to Administration -> System Options. Once there, look under the "New User Experience" section. "Activate New User Experience" checkbox should be ticked.