Event disappearance - Sunbird Lightning Calendar

What can make events disappear from the grid views?

Calendar file checkbox off

In the "Calendars" tab, the checkbox next to the calendar file that contains the events may be off, so no events in that calendar are displayed.

If you add a new event to a calendar whose checkbox is off, it may appear at first and you can see it has been added, but when the view is refreshed again it no longer appears.

Click the calendar file checkbox on to display the events in the calendar file.

Events with zero duration

In Day view and Week view, an event with zero duration (end datetime is same as start datetime) that is after the first event may trigger an error that stops the refresh so no later events are displayed (bug 261890).

Workaround: Set the end time to be later than the start time.