SUMMARY This bug, devastating to usability, causes complete session loss if extreme care is not taken at the lock screen. I'm able to reproduce on both Arch and Kubuntu 23.10, meaning it's not a distro-specific issue. STEPS TO REPRODUCE 1. Enable fingerprint unlocking. This in itself is an ordeal on Plasma and is distro-dependent, usually involving modifying configuration files with root. 2. Engage the lock screen, either by locking the computer or putting it in sleep mode and waking it up. 3. After engaging the lock screen, put the computer to sleep *without unlocking the screen*. 4. Wake the computer up. OBSERVED RESULT KScreenLocker loses the ability to unlock the screen. The "unlock with fingerprint" dialogue is still present (but if it timed out before it was put to sleep, the "timed out" dialogue is still present instead.) However, unlocking with a fingerprint is no longer possible; nothing happens if one tries. Unlocking with a password is no longer possible either; the password prompt can still be input, but clicking on the "enter" key or pressing the enter button does nothing. Switching to a TTY, logging in, and typing "loginctl unlock-session" has no effect. KScreenLocker remains frozen. EXPECTED RESULT KScreenLocker remains functional after going to sleep and waking up. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Kubuntu 23.10 (available in About System) KDE Plasma Version: 5.27.10 KDE Frameworks Version: 5.110.10 Qt Version: 5.15.10 ADDITIONAL INFORMATION In practice, this causes a complete loss of session, including loss of any open data, unless precise care is taken; the user **must** unlock the computer **every time** they wake it from sleep. Opening a laptop lid then immediately closing it again causes data loss. I've lost a couple sessions this way in the last ~1.5 years. I was convinced that switching to Kubuntu might resolve the bug; after discovering it was still present I decided to file a report here.
This was massively improved in Plasma 6 with a near-total rewrite of how fingerprint handling is done. Now you can unlock with your password after the opportunity to unlock with a fingerprint times out due to the underlying fprintd timing out internally. Also note that setting up a fingerprint reader shouldn't be manual ordeal; if it is, this is an indication that the distro doesn't ship with the needed fprint packages pre-installed, which is something you might want to tell them about.