Users report recipients are getting multiple meeting response messages. This issue is caused when iPhone users accept meetings on either their iPhones or iPads with the native iOS Exchange Active Sync. In order to fix this issue, the iOS user (who is sending the meeting acceptance messages) needs to turn off mail and calendar syncing on their mobile device and then turn it back on to stop the flow of the acceptance messages.
On the iOS device:
1. Go to Settings.
2. Tap Accounts and Passwords.
3. Select the account that is sending the repeated accepted meeting invites.
4. From Contacts and Calendar, select the account, turn Mail and Calendar Sync Off and tap Delete from My Phone.