CalDAV only works for first synchronisation, and then stops updateing the calender forever From the same server I can successfully sync cardDAVs contacts, and IMAPs-mail, so I've ruled out network issues.

Furthermore, that same installation also syncs many other users (non-i) -Devices Contacts, Calenders, and Mails, so I've ruled out SOGOs CalDAV implementation.

This Problem is not present on the WinPhones, Androids(with DavDroid), Thunderbird/Lightning, and even Outlook 2010. I kind-of feel stupid now having recommended iDevices in the past.

I tried:


Rebooting normally
Signing out of iCloud, then rebooting
Factory-reset, then configuring the CalDAV first, then the rest.
Opened the non-SSL Port (shudder) to the outside world for testing.
Creating the Calender "twice", Once as Calender, and once as Contactlist


None of those worked, and the last one was impossible through the settings dialog

I'm not quite sure, how to proceed. In the meantime, I bought some cheap androids, so that my users at least have their calendar on the road with them.
Did you check in Settings > Mail, Contacts, Calendars > Fetch New Data > Fetch Every 15 minutes.

Maybe it is set to Manually.