And if I logout, the login screen is still without 'Sign-in options' under my name. However, it appears the PIN is immediately forgotten by Windows because even after I've finished, it still shows only 'Add' under the PIN section of Accounts -> Sign-in options. If I click on 'Add', I am allowed to add a PIN after entering my password. Under Settings, Accounts -> Sign-in options, I now see the option to 'Add' a PIN, as if I had never set a PIN. Now it has reverted to signing in with a password without the option to change back to PIN. The 'Sign-in Options' link is suddenly missing from my Windows 10 login screen.