Mojave login password field disappears

I manage a workspace with 1000+ computers. We put a monolithic image on all the units, and then as users arrive, we add their account to the computer.

To maintain a management account on the computer that the users are unlikely to delete (which many do for some strange reason), we set its User ID to 499 and then use a terminal command to hide all accounts with IDs below 500. Since regular user accounts all automatically receive an ID value beginning at 501, this achieves our goal.

We also set the login to List of Users since occasionally we have to create multiple user accounts.

Under past OS versions, if no User accounts have yet been added, and only the management account exists, the login screen will show a generic icon with a faceless person, and have fields for user name and password below it (since the management account is hidden).

The problem I've discovered today is that under Mojave, after sitting at this login screen for 10-15 seconds, the user name and password fields disappear, and only the icon remains.

No matter what keys you type, or whatever you click on, the fields will not return. It takes a reboot to get the fields back, and you are still subject to that 10-15 second limit before the fields disappear.

When there is a non-hidden account, then there is no problem because the icon for the User (with their name) and a generic icon with "Other..." remain visible. To log into the hidden, I select Other... and then manually enter the user name and password of my management account.

So, my question is are there any options for making the user name and password fields re-appear (other than restarting) if there are no visible user accounts on the computer?