Region.Op.REPLACE is deprecated and therefore the exception is thrown:

[AndroidRuntime] java.lang.IllegalArgumentException: Invalid Region.Op - only INTERSECT and DIFFERENCE are allowed
[AndroidRuntime] at android.graphics.Canvas.checkValidClipOp(Canvas.java:779)
[AndroidRuntime] at android.graphics.Canvas.clipRect(Canvas.java:826)
[AndroidRuntime] at com.telerik.widget.calendar.CalendarFragment.drawRows(CalendarFragment.java:589)
[AndroidRuntime] at com.telerik.widget.calendar.CalendarFragment.render(CalendarFragment.java:259)
[AndroidRuntime] at com.telerik.widget.calendar.CalendarScrollManager$FragmentHolder$LayerView.onDraw(CalendarScrollManager.java:136)
[AndroidRuntime] at android.view.View.draw(View.java:20207)

Provide events raised when a new appointment is created and when an existing appointment is updated/deleted. 

when showing 3 months (last month, present month and the next month) on calendar component, the next month tab is displayed twice. see the attached video

set the MultiDayViewStyle (tried both in code and also in the xaml) and the Appointment settings don't seem to have any effect on Android.

While in DayView (or any other appropriate view), allow for appointments to be draggable to another time slot for rescheduling. 

I've attached a handler to the ViewChanged event of the Calendar component.

The event fires on Android but not on UWP. I've tried changing the view type using the calendar controls and also programatically but the event is not being fired.

If you set SelectedDate when the Calendar control is created, does not take any effect in the UI on iOS. 

As a workaround, set SelectedDate at a later stage.

When RadCalendar is inside Xamarin Forms Tabbed Page. Switching between tabs triggers Calendar SelectionChanged and the calendar DisplayDate is changed. 

Workaround:
the issue could not be reproduced when RadTabView is used and its IsContentPreserved property is set to true.