In the case where some of the columns are hidden and all of the columns' display indexes are changed, applying grouping could result in some of the cells from the columns that have custom CellTemplate to not receive it.

To work this around, you could manually change the widths of the columns by iterating the Columns collection as shown below:

foreach (var column in this.GridView.Columns)
{
    GridViewLength length = column.Width;

    if (length.IsAbsolute)
    {
        column.Width = new GridViewLength(length.Value + 0.00001);
    }
}

The RadGridView control hangs when the frozen columns are enabled and the application is resized. The exact resizing depends on the screen resolution and the exact new size. This was originally recreated on a monitor with 1600x900 resolution 125% DPI and the application was maximized (resized from restored to full screen size). The issue occurs in the Fluent theme. Also, the FluentPalette.Palette.ScrollBarsMode static property should be set to Normal.

To work this around, you can overrider the MeasureOverride method of RadGridView and add the following code:

public class CustomGridView: RadGridView
{
    private static readonly PropertyInfo internalColumnsProp = typeof(GridViewDataControl).GetProperty("InternalColumns", BindingFlags.Instance | BindingFlags.NonPublic);
    private static MethodInfo invalidateColumnsMethod;

    protected override Size MeasureOverride(Size availableSize)
    {
        if (EnableRowVirtualization && !double.IsInfinity(availableSize.Height))
        {
            var internalColumns = internalColumnsProp.GetValue(this);
            if (invalidateColumnsMethod == null)
            {
                invalidateColumnsMethod = internalColumns.GetType().GetMethod("InvalidateColumnWidthsCalculation", BindingFlags.Instance | BindingFlags.NonPublic);                     
            }

            invalidateColumnsMethod.Invoke(internalColumns, null);
        }
        return base.MeasureOverride(availableSize);
    }

The Clear Filters option in the FieldFilterControl cannot be selected when the DefaultOperator1 is set in the FilterOperatorsLoading event of RadGridView. The FieldFilterControl is the element shown under the column header when the FilteringMode property of RadGridView is set to FilterRow. Setting e.DefaulteOperator1 in the FilterOperatorsLoading properly selects the corresponding filter in the drop down, but after that you cannot select Clear Filters when clicking on this option.

To work this around, you can use the CellLoaded event instead of FilterOperatorsLoading. This will allow you to get the FieldFilterControlViewModel and set its SelectedOperatorViewModel property.

private void manualGridView_CellLoaded(object sender, CellEventArgs e)
{
    if (e.Cell is GridViewHeaderCell && e.Cell.Column.UniqueName == "MyColumn")
    {
        Dispatcher.BeginInvoke(new Action(() =>
        {
            var fieldFilter = e.Cell.FindChildByType<FieldFilterControl>();
            var viewModel = (FieldFilterControlViewModel)fieldFilter.DataContext;
            viewModel.SelectedOperatorViewModel = viewModel.AvailableOperatorViewModels.FirstOrDefault(x => x.FilterOperator == FilterOperator.IsLessThan);
        }));
    }
}

The height of the column footer is not updated properly to autofit the footer's content. Actually, this works when the footer content becomes bigger than the current (or the default) value, but if you change the content with a smaller one, the bigger height remains. In other words, the footer height autofits when the content becomes bigger but it doesn't decrease when the content becomes smaller after that.

private void gridView_CellLoaded(object sender, CellEventArgs e)
{
    if (e.Cell is GridViewFooterCell)
    {
        var row = e.Cell.ParentRow;
        Dispatcher.BeginInvoke(new Action(() =>
        {
            var aggregatesList = row.ChildrenOfType<AggregateResultsList>(); // the exact type of children that should be used to get the new height may vary based on your column Footer contents
            if (aggregatesList.Count() > 0)
            {
                var height = aggregatesList.Max(x => x.ActualHeight);

                var cellsPanel = e.Cell.ParentOfType<GridViewCellsPanel>();
                PropertyInfo minRowHeightProp = cellsPanel.GetType().GetProperty("MinRowHeight", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
                object minRowHeightPair = minRowHeightProp.GetValue(cellsPanel);
                PropertyInfo heightProp = minRowHeightPair.GetType().GetProperty("Second");
                heightProp.SetValue(minRowHeightPair, height);
            }
        }));
    }
}

Currently, when you cancel the Filtering event the field filter (displayed when FilteringMode="FilterRow") will clear any entered text and the funnel icon won't change its color (like when the filter is active). Add an option in the Filtering event, similar to the Sorting event which allows you to manually set the sorting state of the column which will affect the UI (showing and changing the sort indicator icon).

In the case with the Filtering event, there should be an option if the funnel icon should be highlighted. In other words the setting should allow you to manually say if the filter is active or not. Also, the input text in the field filter should be preserved and possible an option to change this value may be added in the event arguments. This will allow you to implement custom filtering and keep the UI state of the field filter.