帳票出力時、グループ化によって画像セルが結合される際、画像がセルの中央ではなく上部に配置されます。

この問題はバージョン7.1.3で修正されました。
※修正版を適用しない場合の回避方法は以下の通りです。

ProcessTemplateメソッドの実行後に下記の処理を呼び出す方法にて回避できます。

static void Main(string[] args)
{
    ・・・
    workbook.ProcessTemplate();
    ProcessShapeWithCellAlignment(workbook);　//回避策
    workbook.Save("test.xlsx");
}
 
//回避策
private static void ProcessShapeWithCellAlignment(Workbook workbook)
{
    foreach (var worksheet in workbook.Worksheets)
    {
        foreach (var shape in worksheet.Shapes)
        {
            var leftTopCell = shape.TopLeftCell;
            var rightBottomCell = shape.BottomRightCell;
 
            var entireMergeArea = leftTopCell?.EntireMergeArea;
 
            if (leftTopCell != null && rightBottomCell != null &&
                ((leftTopCell.Row == rightBottomCell.Row &&
                leftTopCell.Column == rightBottomCell.Column) ||
                (entireMergeArea != null && rightBottomCell.Row >= entireMergeArea.Row &&
                rightBottomCell.Row <= entireMergeArea.LastRow &&
                rightBottomCell.Column >= entireMergeArea.Column &&
                rightBottomCell.Column <= entireMergeArea.LastColumn)))
            {
                var rect = CellInfo.GetAccurateRangeBoundary(entireMergeArea != null ? entireMergeArea : leftTopCell);
                if (leftTopCell.HorizontalAlignment == HorizontalAlignment.Left)
                {
                    // Adjust the position of the shape to align left.
                    shape.LeftInPixel = rect.Left;
                }
                else if (leftTopCell.HorizontalAlignment == HorizontalAlignment.Center)
                {
                    // adjust the position of the shape to center
                    shape.LeftInPixel = rect.Left + (rect.Right - rect.Left - shape.WidthInPixel) / 2;
                }
                else if (leftTopCell.HorizontalAlignment == HorizontalAlignment.Right)
                {
                    // adjust the position of the shape to right
                    shape.LeftInPixel = rect.Right - shape.WidthInPixel;
                }
 
                if (leftTopCell.VerticalAlignment == VerticalAlignment.Top)
                {
                    // adjust the position of the shape to top
                    shape.TopInPixel = rect.Top;
                }
                else if (leftTopCell.VerticalAlignment == VerticalAlignment.Center)
                {
                    // adjust the position of the shape to center
                    shape.TopInPixel = rect.Top + (rect.Bottom - rect.Top - shape.HeightInPixel) / 2;
                }
                else if (leftTopCell.VerticalAlignment == VerticalAlignment.Bottom)
                {
                    // adjust the position of the shape to bottom
                    shape.TopInPixel = rect.Bottom - shape.HeightInPixel;
                }
            }
        }
    }
}