Hibernate Security Problem

We use a few 5070s with ThinOS as Kiosk Thinclients in our factories, where Workers without Domain Accounts use specific Citrix Apps.
For this to work a fixed User and Password is configured on the Thinclient via WMS and does Auto-Login with no Option for the Users to change the credentials or manipulate the logon process.
But some Users found out that if you hibernate the 5070 and wake it up again the Password Field of the Login Form is suddenly editable.
They put in wrong Passwords to lock the Account, and argue they can't do their work because of faulty Thinclients.
We found no way to disable Hibernate or hide the Logon-Dialogue on Wakeup from Hibernate.
ThinOS and WMS on latest Version.

What are our options?