As of a recent update to my Kubuntu 20.04 laptop, the lock screen can no longer be passed through with just typing the password and hitting enter. The mouse must first be moved to get the password field to display, and then the password can be entered. (Well, pressing Tab twice and then Shift+Tab three times also enables the input without using the mouse, but that is not an acceptable user experience). 


STEPS TO REPRODUCE
0. System setup: I have been able to reproduce the problem in a Kubuntu 20.04.3 virtual machine.
    1. Install Kubuntu 20.04.3. At this point when locking the expected behavior will be observed.
    2. Apply updates. At this point the bug is evident, even without a restart.
1. Lock the screen (e.g. Meta+L).
2. Without moving the mouse beforehand, hit a key (e.g. try to enter your password). NOTE: If the mouse is moved first the keyboard input works.

OBSERVED RESULT
Nothing happens on pressing keys, with the exception of hitting Tab twice. At that point, the lock screen fields beyond the clock are shown, but to get back to the password field I have to Shift+Tab three times.

EXPECTED RESULT
Pressing a key should show the login fields and be provided as input to the password field, as was the case before the update.

SOFTWARE/OS VERSIONS
Windows: N/A
macOS: N/A
Linux/KDE Plasma: Kubuntu 20.04
KDE Plasma Version: 5.18.8
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8

ADDITIONAL INFORMATION
You can see that this has effected several users here: https://www.reddit.com/r/Kubuntu/comments/sw6ey1/keyboard_inactive_to_awake_from_screen_lock/