After a clean iOS 7 upgrade (restored as new), we found that we couldn't add calendar events and many of the events from the past were missing. Apparently, there are a couple of reasons this happens. If you're facing a similar issue, you might find this to be useful.
The error usually boils down to syncing issues. If you haven't synced your Calendar or if the events synced have an upper time cap, you get these strange errors that prevent events from being added or past events from showing up.
Sync All Events
If you upgraded to iOS 7 on an iDevice and find that events are missing from the Calendar, it's most probably because of a sync issue. The very first thing you are going to try is this:
Go to Settings → iCloud and turn ON Calendars. This makes sure your iCloud calendars are synced to the device.
But this isn't enough. Deep within Settings, you have one more configuration to set.
- Go to Settings → Mail, Contacts, Calendars
- Under Calendars, tap on Sync
- Select All Events
This makes sure all events from the past are synced and not just a few from the recent past. More often than not, having a different selection in Sync Events leads to a lot of confusion.
Make Sure Calendars Are Synced On All Devices
Rarely – or may occasionally – people come up with Calendar issues on one device but the real problem lies in other devices. For instance, if you updated your iPad but it's not showing events you created on your iPhone, you must also make sure that the calendar is synced from your iPhone.
As for testing sync issues, you can always use http://icloud.com to check the status of sync between your iDevice and the iCloud server.