For the upcoming release of oC 9.0 the CalDAV and CardDAV backends where merged into ownCloud core like described here:
https://forum.owncloud.org/viewtopic.php?f=38&t=32735
As a result the old apps from oC 8.2 and previous are now "deprecated" and "unmaintained" (The contacts app was even unmaintained before).
If you find an issue in one of those apps you can try to report it to:
https://github.com/owncloudarchive/calendar/issues
https://github.com/owncloudarchive/contacts/issues
However you should note that there will be very likely no fix provided for any of the existing or new issues.