On screen keyboard on lock screen, after user switchung (Win10)

Question

We use two Windows accounts (a standard user and an administrator).

When logging in to the user account and switching to the administrator account using "fast user switching", the on-screen keyboard no longer opens in the lock screen when typing in the password field. We have tested the problem with different devices (MS Surface, DELL, etc.).

We were able to reproduce the problem with all different devices. Only after a complete reboot was it possible to get the on-screen keyboard.

Note: The devices are in tablet mode, without a hardware keyboard.