Touchdown 9.0.00412 on Galaxy S7. Exchanged hosted by Microsoft through Office 365.
Recently dimissing Appointments through the notifications do not work - or stay dismissed.
That is, meeting reminders appear in the notifications. I pull down to get access to the larger notification screen and click "Dismiss". However the event never stay dismissed. 15 minutes later they remind me again, dismiss, reminder, dismiss, reminder.
For example it's 4pm and I've dismissed the same meeting from 9-10am countless times today. This has occur for many many days now.