Dropdownlist does not hold selected value when use pagination in .NET core 2.2

Public async Task<IActionResult> Index(string searchText, string currentFilter, int? page)
    {

            int selectedPage = page ?? 1;
            int bypassCount = (selectedPage - 1) * _pagingOptions.PageSize;

            if (searchText != null)
            {
                page = 1;
            }
            else
            {
                searchText = currentFilter;

            }

            ViewBag.CurrentFilter = searchText;

    }

<form asp-action="Index" method="get">

            <select class="custom-select" asp-for="searchText" value="@(ViewBag.CurrentFilter)">
                <option value="">All</option>
                <option value="AA">AA</option>
                <option value="AE">AE</option>
                <option value="AR">AR</option>
            </select>

         <div class="col-md-12">
            <button class="btn btn-primary" type="submit">Search</button>
         </div>                
        </form>

    <table class="table">
        <thead>
            <tr >
                <th>Resent</th>
                <th>Resent Date</th>
                <th>Created Date</th>
            </tr>
        </thead>
        <tbody>
            @if (Model.Items.TotalItemCount > 0)
            {
                @foreach (var item in Model.Items.ToList())
                {                     
                        <td>@Html.DisplayFor(modelItem => resentString)</td>
                        <td>@Html.DisplayFor(modelItem => resentDateString)</td>
                        <td>@Html.DisplayFor(modelItem => createdDateString)</td>
                    </tr>

                }
            }

        </tbody>
    </table>
</div>

            @if (Model.Items.PageCount > 1)
            {
                @Html.PagedListPager(Model.Items, page => Url.Action("Index", new { page = page, currentFilter = ViewBag.CurrentFilter})
            }