Screen never locking (KDE Plasma)

[Pistos]

After any given reboot of this system, the automatic screen locking after inactivity timeout works fine for the first few days, but then eventually it never activates on its own. Manual screen locking works fine. Anyone know why this might be the case? Is there a /proc/* thingie I can use to see what the system thinks the current inactivity time is?

[Pistos]

I worked around the problem using cron and `qdbus`.