SUMMARY I opened KOrganizer to edit an event that I'd dealt with, and thus didn't need to be reminded of any more. At the time, it had an active reminder that was suspended for 30 minutes, and a number of scheduled reminders for the next few days. When I double-clicked on the event, the event editor didn't open as it normally does. Double-clicking on other events did not open the event editor either, and neither did selecting events and choosing "Edit" in the Action menu. The mouse-over information for the event displayed OK, so it's not that the event information could be accessed at all. Looking at the .xsession-errors log, I could see the following error message occuring every time I attempted to open the editor: org.kde.pim.incidenceeditor: free slot calculation: invalid range. range( 0 ) / mSlotResolutionSeconds( 900 ) = 0 As a workaround, I first tried restarting KOrganizer by selecting "Quit" in its main meny, and launching it again. The problem persisted. I recalled that another spurious KOrganizer malfunction corrected itself when I restarted Akonadi, so I tried that ("akonadictl stop", waiting for a few seconds, then "akonadictl start"). This did the trick, and I no longer see the problem. I noticed that the error message quoted above still showed up every time I opened the editor for an event, so maybe it's unrelated to the actual problem. STEPS TO REPRODUCE I tried to reproduce the problem, but couldn't. I've only seen it once, but I've seen several other spurious KOrganizer problems that resolve when Akonadi is restarted. Perhaps every other week or so in a long-running session. Despite being irreproducible, I thought I'd report it, since a non-technical user would not think of restarting Akonadi, resulting in a quite serious persisting problem. If nothing can be done to fix the bug, then at least the problem and a workaround can be found in this report. OBSERVED RESULT Event editor didn't open. EXPECTED RESULT Event editor to open. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Kubuntu 18.04 KDE Plasma Version: 5.12.8 KDE Frameworks Version: 5.44.0 Qt Version: 5.9.5 ADDITIONAL INFORMATION Reported this is a KOrganizer / incidence editor bug, since that's where I experienced the problem as an end-user. I don't know whether the fact that restarting Akonadi helped means that the problem is more likely to be there, or in some other general infrastructure. Please edit if you know better.