The exception is being caused by the fact that not all your grid cells are populated. You have to add a check to querycellinfo to avoid trying to use a null GridStyleInfoStore. Also, you are using the row and column headers. In this case, you would need to use row and col zero in the event as well.
private void gridControl1_QueryCellInfo(object sender, Syncfusion.Windows.Forms.Grid.GridQueryCellInfoEventArgs e)
{
if(_flipped && e.ColIndex > -1 && e.RowIndex > -1)
{
if(this.gridControl1.Data[e.ColIndex, e.RowIndex] != null)
{
e.Style.ModifyStyle(this.gridControl1.Data[e.ColIndex, e.RowIndex], Syncfusion.Styles.StyleModifyType.Override);
}
e.Handled = true;
}
}