For quite some time now, KDE has intermittently been unable to go to sleep. It will either go to a black screen with the cursor still showing, and the computer running, or it will show a half frozen sddm looking screen with the computer still running. The computer, in both cases, will be wholly unresponsive, and the only way to get out of it is to forcefully shutdown the PC by, for example, holding the power button.
My suspicion is that a kernel update broke it and that downgrading to LTS (or even an older LTS) kernel would fix it. I didn't bother to troubleshoot further because I don't need suspend that badly (desktop).