New Outlook: EventType.SelectedItemsChanged does not trigger reliably about office-js

[ottD]

We are facing the same issue. The Office.EventType.SelectedItemsChanged event consistently fails to fire on OWA and new Outlook when changing the email selection from one to two selected emails just as @senden9 has outlined. This bug significantly impacts add-ins supporting item multi-select as the selected emails shown in the add-in task pane do not reflect the actual email selection in the user's mailbox which is confusing to users. The suggested work arounds using a timer or subscribing to the Office.EventType.ItemChanged event are insufficient as they defeat the purpose of the Office.EventType.SelectedItemsChanged event which is specifically designed to deal with item selection changes in item multi-select add ins as documented here