The Id of Opening does not fire the bound command.  This is on iOS only, Android does not suffer from this problem

        <telerik:RadSideDrawer DrawerLocation="Left"
                               DrawerTransitionType="Push"
                               x:Name="MainDrawer"
                               Margin="{OnPlatform iOS='-1,0', Default='0'}"
                               VerticalOptions="FillAndExpand"
                               IsOpen="{Binding MainDrawerOpen, Mode=OneWayToSource}"
                               DrawerTransitionFadeOpacity="0">
            <telerik:RadSideDrawer.Commands>
                <telerik:SideDrawerUserCommand Id="Opening"
                                               Command="{Binding Source={x:Reference Home}, Path=DrawerOpeningCommand}" />

                <telerik:SideDrawerUserCommand Id="Closed"
                                               Command="{Binding Source={x:Reference Home}, Path=DrawerClosedCommand}" />
            </telerik:RadSideDrawer.Commands>