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macrumors newbie
Original poster
Jul 22, 2017
On December 12, 2016 (iOS Version 10.2.0), I began experiencing intermittent iPhone Calendar alerts problems. Everything worked perfectly before this update. I have an iPhone 5s and always install the latest iOS update. Intermittently, the alert does not occur at all. These are the actions that I have tried.

09 JAN 2017
Reset All Settings. No change.

03 FEB 2017
Added a default alert time for all created events. No change.

10 FEB 2017
Turned on Time Zone Override, and Reset Location & Privacy. No change.

15 FEB 2017
Turned off instantaneous iCloud syncing. No change.

19 APR 2017
Reinstalled Calendar app. No change.

20 APR 2017
Reset phone, and restored from backup from laptop through iTunes. No change.

18 JUN 2017
Reset phone, setup as new, and just synced iCloud. No change.

This is a hard problem because it is intermittent and thus cannot be recreated. I have tried. However, if Calendar alerts do not work all the time, that is a big problem because what is the point of using them if they are not reliable.

I need to be able to consistently recreate the problem before Apple will take it seriously. Otherwise, technical support representatives will just continue to assume that it is my fault rather than a bug in the code. My current theory is that the problem occurs when you set an alert, it works as it should, and then you change it so that it occurs again when the event is still closer to the current time, but I have sort of disproven that, so the problem may involve a second variable (e.g., phone is locked, WiFi connectivity is lost, repeating events only, etc) or be something else entirely. Is anyone else experiencing a similar problem? Does anyone have any ideas on how to recreate the problem?


macrumors 601
Jul 24, 2008
Pacific Northwest, US
Yikes. That has to be frustrating. I assume you're on 10.3.3 now? Sorry, when you say you reinstalled the Calendar app, what exactly does that mean? Is anything else touching your calendar, like syncing to a third party product, e.g., ActiveSync to Microsoft Exchange or editing your calendar on a Mac or PC via iCloud?


macrumors newbie
Original poster
Jul 22, 2017
Hi. Thanks for the empathy; I needed it. I am now on 10.3.2. (I have not received a notification to update to 10.3.3 yet.) I was told to delete the Calendar app just like you delete any other app. I then installed it again from the iTunes Store. I was told that this does not do the same thing as uninstalling and reinstalling a nonnative app because Calendar is intimately linked to iOS. Nevertheless, I was told to try it and did.

No. No third party products, and I am not editing my Calendar via iCloud.

The only other lead that I can supply is that I've noticed that the clock within the Calendar app sometimes lags behind the clock on the OS. See the attached screenshots that I took when I was able to capture one instance of this problem. My hunch is that there is some bug that prevents the Calendar app clock from synchronizing with the OS clock. The alert is not given because, by the time that the Calendar app clock catches up with the OS clock, the time for the alert has passed.


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macrumors newbie
Dec 15, 2016
I have had this problem for years and stumbled across the fix the other day. I had an old iPad on my account that the battery had died and date/time had reset to 01 Jan 1970. After resetting date time, charging and then deleting from my iCloud account my iPhone alerts have worked as advertised.

Have a look at your iCloud account for old devices and delete them. Hope this helps.

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