Garante que o table header view vai ser redimensionado corretamente para encapsular a view atribuida

UITableView+AtribuirTableHeaderView.cs

using UIKit;

namespace App.iOS.Extensions
{
    //https://stackoverflow.com/questions/5484493/changing-the-height-of-a-tableheaderview-hides-the-cells/5764819#5764819
    public static class UITableViewAtribuirTableHeaderView
    {
        private static bool VersaoIosBugadaQueNaoAtualizaOTamanhoCorretamenteDoTableHeaderView =>
            !UIDevice.CurrentDevice.CheckSystemVersion(9, 0);

        public static void AtribuirTableHeaderView(this UITableView @this, UIView view)
        {
            if (VersaoIosBugadaQueNaoAtualizaOTamanhoCorretamenteDoTableHeaderView)
            {
                AtribuiTableHeaderViewRespeitandoTamanhoDaViewAtribuida(@this, view);
                return;
            }

            @this.TableHeaderView = view;
        }

        private static void AtribuiTableHeaderViewRespeitandoTamanhoDaViewAtribuida(UITableView tableView, UIView view)
        {
            tableView.TableHeaderView = view;
            view.SizeToFit();
            tableView.TableHeaderView = view;
        }
    }
}