Question about how button events work in CollectionView vs. outside

[DreamDelerium]

I have a Xamarin form where I have a list and two buttons. What I am seeing is that, depending where the buttons are, the model loads differently. Depending on where the buttons reside in the Xaml page, the load events change:

1.  When the buttons are within CollectionView (in the footer), and the page loads, first the ViewModel's constructor loads then the Query Parameter setters load (CurrentMonth set then CurrentYear set) are called.
2.  When the buttons are outside the CollectionView, first the ViewModel's constructor loads then ValidatePrevious method is called and then ValidateNext method is called, skipping the Query Parameter Getter/Setter methods.

Why does the placement of the buttons in the Xaml file change the order of operations in my ViewModel? And, how do I ensure that the Query Parameter setters are called first, regardless of where the buttons reside?

Here is my Xaml code:

RewardsPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyApp.Views.RewardsPage"
             Title="{Binding Title}"
             xmlns:local="clr-namespace:MyApp.ViewModels"  
             xmlns:model="clr-namespace:MyApp.Models" x:DataType="local:RewardsViewModel"
             x:Name="BrowseItemsPage">    
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="650" />
        </Grid.RowDefinitions>
        <CollectionView x:Name="ItemsListView"
                ItemsSource="{Binding Items}"
                SelectionMode="None" Grid.Row="1" >            
            <CollectionView.ItemTemplate>
                <DataTemplate>
                    <StackLayout Padding="10" x:DataType="model:RewardModel">
                        <Label Text="{Binding id, StringFormat='ID: {0}'}" 
                            LineBreakMode="NoWrap" 
                            Style="{DynamicResource ListItemTextStyle}" 
                            FontSize="16" />
                         <!--other labels removed for brevity-->
                    </StackLayout>
                </DataTemplate>
            </CollectionView.ItemTemplate>
            <CollectionView.Footer>
                <StackLayout Orientation="Horizontal">
                    <Button Text="Previous Month" Command="{Binding PreviousMonthCommand}" HorizontalOptions="FillAndExpand"></Button>
                    <Button Text="Next Month" Command="{Binding NextMonthCommand}" HorizontalOptions="FillAndExpand"></Button>
                </StackLayout>
            </CollectionView.Footer>
        </CollectionView>
    </Grid>
</ContentPage>

The code works fine here. But, if I move the StackLayout from the CollectionView.Footer to its own grid row, like this:

</CollectionView>
   <!--other labels removed for brevity-->
</CollectionView>
<StackLayout Orientation="Horizontal" Grid.Row="2">
   <Button Text="Previous Month" Command="{Binding PreviousMonthCommand}" HorizontalOptions="FillAndExpand"></Button>
    <Button Text="Next Month" Command="{Binding NextMonthCommand}" HorizontalOptions="FillAndExpand"></Button>
</StackLayout>

Then the code in my RewardsViewModel executes in a different order. Here is my RewardsViewModel code (simplified):

[QueryProperty(nameof(CurrentMonth), nameof(CurrentMonth))]
[QueryProperty(nameof(CurrentYear), nameof(CurrentYear))]
public class RewardsViewModel: BaseViewModel
{
    public ObservableCollection<RewardModel> Items { get; }
    private List<MonthModel> months;
    private int _current_year;
    private int _current_month;
    public Command PreviousMonthCommand { get; }
    public Command NextMonthCommand { get; }
    
    public RewardsViewModel()
    {              
        Items = new ObservableCollection<RewardModel>();
        PreviousMonthCommand = new Command(OnPrevious, ValidatePrevious);
        NextMonthCommand = new Command(OnNext, ValidateNext);            
    }
    public int CurrentYear
    {
        get
        {
            return _current_year ;
        }
        set
        {
            _current_year = value;               
            LoadItems();
        }
    }
    public int CurrentMonth
    {
        get
        {
            return _current_month;
        }
        set
        {
            _current_month= value;                
            LoadItems();
        }
    }
 
    public void LoadItems()
    {
        IsBusy = true;
        //do stuff
    }
    private bool ValidatePrevious()
    {
         //do stuff to validate and return true or false 
    }
    private bool ValidateNext()
    {  
        //do stuff to validate and return true or false          
    }
    private void OnPrevious()
    {
       //do stuyff
    }
    private void OnNext()
    {
        //do stuff
    }
}

This page is called, from the previous page, that loads this page, passing in the Query Parameters:

async void OnItemSelected(MonthModel item)
{
   if (item == null)
      return;
   await Shell.Current.GoToAsync($"{nameof(RewardsPage)}?{nameof(RewardsViewModel.CurrentYear)}={CurrentYear}&CurrentMonth={SelectedItem.month}");
}

If it helps, the RewardsVeiwModel extends BaseViewModel. That code is:

public class BaseViewModel : INotifyPropertyChanged
 {       
     bool isBusy = false;
     public bool IsBusy
     {
         get { return isBusy; }
         set { SetProperty(ref isBusy, value); }
     }

     string title = string.Empty;
     public string Title
     {
         get { return title; }
         set { SetProperty(ref title, value); }
     }

     protected bool SetProperty<T>(ref T backingStore, T value,
         [CallerMemberName] string propertyName = "",
         Action onChanged = null)
     {
         if (EqualityComparer<T>.Default.Equals(backingStore, value))
             return false;

         backingStore = value;
         onChanged?.Invoke();
         OnPropertyChanged(propertyName);
         return true;
     }

     #region INotifyPropertyChanged
     public event PropertyChangedEventHandler PropertyChanged;
     protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
     {
         var changed = PropertyChanged;
         if (changed == null)
             return;

         changed.Invoke(this, new PropertyChangedEventArgs(propertyName));
     }
     #endregion
 }