I am unsure of when it started, but it got bad enough for me to complain on the users mailing list about it in November last year (http://lists.kolab.org/pipermail/users/2018-November/021600.html). I have done a little more poking around as I was investigating why the kolab-webclient package wouldn't update and found the following in my apache error.log:
[Fri Feb 15 10:14:26.434193 2019] [core:notice] [pid 1770] AH00094: Command line: '/usr/sbin/apache2' unnamed app(13066) KSystemTimeZonesPrivate::readConfig: readConfig(): local zone= "UTC" unnamed app(13066) KSystemTimeZonesPrivate::readZoneTab: readZoneTab( "/usr/share/zoneinfo/zone.tab" ) Critical: /usr/src/packages/BUILD/src/xcalconversions.h 1914: Unhandled exception schema exception :1:1 error: invalid document structure Critical: /usr/src/packages/BUILD/src/xcalconversions.h 1943: Failed to parse calendar! unnamed app(13068) KSystemTimeZonesPrivate::readConfig: readConfig(): local zone= "UTC" unnamed app(13068) KSystemTimeZonesPrivate::readZoneTab: readZoneTab( "/usr/share/zoneinfo/zone.tab" ) Critical: /usr/src/packages/BUILD/src/xcalconversions.h 1914: Unhandled exception schema exception :1:1 error: invalid document structure Critical: /usr/src/packages/BUILD/src/xcalconversions.h 1943: Failed to parse calendar!
Searching for the redConfig message turns up a bug from 2015 (https://lists.kolabsys.com/pipermail/bugzilla/2015-March/023861.html) but I cannot find any conversation on it because issues.kolab.org is no longer with us. Has this been solved or is there an open issue that I cannot find?