Instance of calendar appointment is missing or duplicated on ActiveSync client

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Symptoms

When a user syncs a mailbox on an iOS device with a Microsoft Exchange ActiveSync client, the calendar on the device may be missing one or more appointments. These appointments are available when you view the calendar from Outlook or Outlook Web App (OWA). Also, there may be duplicate instances of the appointment in the calendar when the meeting is accepted from the device.

This issue occurs in the following scenario:

The organizer sends a recurring meeting to one or more attendees.
The organizer adds an attendee to an instance of the recurring meeting.
The organizer adds the attendee to a second instance of the recurring meeting.

In this scenario, the new attendee sees only one instance of the meeting on his or her calendar.

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Cause

This issue occurs because of the manner in which the ActiveSync client handles calendar items.

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Resolution

Apply the iOS 8.2 update. Apple has documented the issue in the following article from the Apple Knowledge Base:
https://support.apple.com/kb/DL1794?locale=en_US&viewlocale=en_US

If this issue is not resolved by applying the iOS update, customers should contact the mobile device vendor.

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More Information

Each appointment has a unique global object identifier (GOID) value. When a user is sent an instance of a recurring meeting, the GOID contains the date and time information for that specific instance. This means that these two instances of the recurring meeting are created in the user's calendar by using two unique GOID values. You can find these GOID values in the following UID element from the ActiveSync mailbox log.

Note In these examples, the UID is broken into segments to show the difference in the date values. The date segment in each instance is commented.

Instance 1

<ServerId>1:19</ServerId>
  <ApplicationData>
  <TimeZone xmlns="Calendar:">LAEAACgAVQBUAEMALQAwADUAOgAwADAAKQAgAEUAYQBzAH///w==</TimeZone>
  <DtStamp xmlns="Calendar:">20141030T134707Z</DtStamp>
  <StartTime xmlns="Calendar:">20141106T150000Z</StartTime>
  <Subject xmlns="Calendar:">Multiple instances of this meeting</Subject>
  <UID xmlns="Calendar:">
    040000008200E00074C5B7101A82E008
    07DE0B06  //Represents the date for this instance of the appointment.
    A04A2A4F26F4CF01
    0000000000000000
    10000000
    68C95CC61952A044A7FAD2D294C0E07C</UID>

Instance 2

<ServerId>1:20</ServerId>
  <ApplicationData>
  <TimeZone xmlns="Calendar:">LAEAACgAVQBUAEMALQAwADUAOgAwADAAKQAgAEUAYQBzAHQAZQByAG4A///w==</TimeZone>
  <DtStamp xmlns="Calendar:">20141030T134839Z</DtStamp>
  <StartTime xmlns="Calendar:">20141120T150000Z</StartTime>
  <Subject xmlns="Calendar:">Multiple instances of this meeting</Subject>
  <UID xmlns="Calendar:">
    040000008200E00074C5B7101A82E008
    07DE0B14  //Represents the date for this instance of the appointment.
    A04A2A4F26F4CF01
    0000000000000000
    10000000
    68C95CC61952A044A7FAD2D294C0E07C</UID>

Third-party information disclaimer

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.

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