After the recent updates in Stretch I have experienced a reliable problem with KOrganizer.
On initial start after login, it does not display items from the Desktop Calendar (${HOME}/.kde/share/apps/korganizer/std.ics). After some time (yet to be determined, but more than a few seconds), a restart of KOrganizer will display everything fine. I have yet to investigate (perhaps with Akonadi Console?), but wondered if anybody else was seeing the same problem? Andy.