My issues seems to be present in 10.13 and 10.14.
We have the login window configured to show text fields for username and password. If a user logs out, the normal login window will show up. If a user restarts the machine, it will show the last logged in user but only gives a password field, if you click help it asks to reset your PW using your recovery key. At the bottom there is only a restart and shutdown button.
I am 100% sure file vault is causing this and it is troublesome for shared Macs. We can't expect a user to log out every time, they will shutdown the Mac most likely. There is not user switch button on the screen, I have it configured to allow user switch but it's not there. Is there something I am missing regarding this login window or FileVault in general?