Events Invisible or Missing (Yahoo)
If your events get randomly deleted or even gone completely, there's a 99% chance you are syncing with Yahoo Calendar.
To check if you sync with Yahoo
- Tap Calendars
- Check if Yahoo is mentioned here somewhere
Syncing with Yahoo Calendar can cause random deletion of events on mobile devices.
Please be aware that this is not an app issue, but a Yahoo issue!
Yahoo gave the following possible solution: https://discussions.apple.com/thread/3186946?start=90&tstart=0.
In short: Yahoo advices to not sync via CalDAV, but to use the built-in Yahoo option instead when setting up a Yahoo account on the iOS via System Settings, see Setup Calendar Synchronization