I have an iPhone 6s Plus. I have newest operating system & just did most recent update tonight (calendar items disappeared before that update). Over the last 8 weeks or so I have periodically lost ALL calendar items. It seems to happen only when I hit 'later or snooze' on an event that pops up as a reminder. Then absolutely every item on the calendar (other than default holidays etc) is gone. And of course when something pops up & you are busy you hit snooze/later automatically! A couple weeks ago I installed Tiny Calendar and had begun using that instead. Tonight I had a pop-up on that & hit the later button and everything was gone from Tiny Calendar, as well as the default calendar. I did a ton of searching & only seem to come up with the suggestion (repeatedly) to change the sync to keep all items. That was mentioned several times but more in reference to losing 'older' items. Supposedly everything would reappear once you opened calendar again. But nothing came back (new or old). Anyone have any suggestions on this?