Hi,
I'm running KOrganizer 5.2.3 on KDE frameworks 5.28.0 on Devuan Linux (Ascii). I'm in the UK using the "Europe/London" time zone. Local KOrganizer calendars are fine.

I'm also using shared calendars on a Kronolith (Horde) backend over CalDAV. This is also running on a Devuan Linux box (Jessie). The CalDAV calendar is sync'd to my Android phone and tablet using the Android "CalDAV-sync" application as well as to KOrganizer.

If I create an event using the Horde Kronolith web UI, it syncs to KOrganizer, phone and tablet at the correct time. If I look at the kronolith calendar entries in its MySQL database, the event is there with correct timezone and time. All fine so far - KOrganiser, Kronolith, phone and tablet all show the same time.

If I create an event using KOrganizer in the CalDAV calendar, it appears at the right time in KOrganizer but shows up 1 hour earlier in Kronolith, phone and tablet. If I check the CalDAV MySQL database, the start and end times for the event match what Kronolith, phone and tablet show - one hour earlier than that shown by KOrganizer. If I edit the event in Kronolith (e.g. changing the description), when I sync the calendar back to KOrganizer, the times are now consistent. KOrganizer now shows the event at the earlier time, matching the database time, and KOrganizer, Kronolith, phone and tablet show the same time.

What is very weird is that this used to work in 2017. When I look back through the calendar, sorting events in the MySQL database by modified time, all events created or modified in 2017 are correct. All the events created in 2018 by KOrganizer are 1 hour earlier in the database.

Any suggestions as to where I could go digging to help diagnose the root cause?

Thanks in advance.