@using System.ComponentModel.DataAnnotations

@inject IJSRuntime js

<label><TelerikCheckBox @bind-Value="@EnableScrollWorkaround" /> Enable Workaround</label>

<TelerikGrid Data="@GridData"
             EditMode="@GridEditMode.Inline"
             OnAdd="@OnGridAdd"
             OnUpdate="@OnGridUpdate"
             OnCreate="@OnGridCreate"
             Width="700px"
             Height="400px"
             Class="grid-class">
    <GridToolBarTemplate>
        <GridCommandButton Command="Add">Add Item</GridCommandButton>
    </GridToolBarTemplate>
    <GridColumns>
        <GridColumn Field="@nameof(Product.Name)" Width="200px" Locked="true" />
        <GridColumn Field="@nameof(Product.Price)" Width="200px" />
        <GridColumn Field="@nameof(Product.Quantity)" Width="200px" />
        <GridCommandColumn Width="200px" Locked="true">
            <GridCommandButton Command="Edit">Edit</GridCommandButton>
            <GridCommandButton Command="Save" ShowInEdit="true">Save</GridCommandButton>
            <GridCommandButton Command="Cancel" ShowInEdit="true">Cancel</GridCommandButton>
        </GridCommandColumn>
    </GridColumns>
</TelerikGrid>

<script suppress-error="BL9992">

    function scrollGridToTop() {
        var gridContentArea = document.querySelector(".grid-class .k-grid-content");
        if (gridContentArea) {
            gridContentArea.scrollTop = 0;
        }
    }

</script>

@code {
    private bool EnableScrollWorkaround { get; set; } = true;

    private List<Product> GridData { get; set; } = new();

    private int LastId { get; set; }

    private async Task OnGridAdd(GridCommandEventArgs args)
    {
        if (EnableScrollWorkaround)
        {
            await js.InvokeVoidAsync("scrollGridToTop");
        }
    }

    private void OnGridUpdate(GridCommandEventArgs args)
    {
        var updatedItem = (Product)args.Item;
        var originalItemIndex = GridData.FindIndex(i => i.Id == updatedItem.Id);

        if (originalItemIndex != -1)
        {
            GridData[originalItemIndex] = updatedItem;
        }
    }

    private void OnGridCreate(GridCommandEventArgs args)
    {
        var createdItem = (Product)args.Item;

        createdItem.Id = ++LastId;

        GridData.Insert(0, createdItem);
    }

    protected override void OnInitialized()
    {
        for (int i = 1; i <= 30; i++)
        {
            GridData.Add(new Product()
            {
                Id = ++LastId,
                Name = $"Product {LastId}",
                Quantity = (short)Random.Shared.Next(0, 1000),
                StartDate = DateTime.Now.AddDays(-Random.Shared.Next(60, 1000)),
                IsActive = LastId % 4 > 0
            });
        }
    }

    public class Product
    {
        public int Id { get; set; }
        [Required]
        public string Name { get; set; } = string.Empty;
        public decimal Price { get; set; }
        public int Quantity { get; set; }
        public DateTime StartDate { get; set; }
        public bool IsActive { get; set; }
    }
}

    .k-grid .k-grouping-header {
        padding: 0;
        border-bottom-width: 0;
        gap: 0;
    }

        .k-grid .k-grouping-header::before {
            margin: 0;
        }

    .k-grid .k-grouping-header .k-grouping-drop-container {
        margin: 0;
    }

@using Telerik.DataSource

<h2>No Aggregates</h2>

<p><code>OnStateInitCounter1:</code> @OnStateInitCounter1</p>
<TelerikGrid Data="@GridData"
             TItem="@SampleModel"
             Groupable="true"
             OnStateInit="@OnGridStateInit1">
    <GridAggregates>

    </GridAggregates>
    <GridColumns>
        <GridColumn Field="@nameof(SampleModel.Name)" />
        <GridColumn Field="@nameof(SampleModel.GroupName)" />
    </GridColumns>
</TelerikGrid>

<h2>With Aggregates</h2>

<p><code>OnStateInitCounter2:</code> @OnStateInitCounter2</p>
<TelerikGrid Data="@GridData"
             TItem="@SampleModel"
             Groupable="true"
             OnStateInit="@OnGridStateInit2">
    <GridAggregates>
        <GridAggregate Field="@nameof(SampleModel.Name)" Aggregate="@GridAggregateType.Count" />
    </GridAggregates>
    <GridColumns>
        <GridColumn Field="@nameof(SampleModel.Name)" />
        <GridColumn Field="@nameof(SampleModel.GroupName)" />
    </GridColumns>
</TelerikGrid>

<h2>With Aggregates and Workaround</h2>

<p><code>OnStateInitCounter3:</code> @OnStateInitCounter3</p>
<TelerikGrid Data="@GridData"
             TItem="@SampleModel"
             Groupable="true"
             OnStateInit="@OnGridStateInit3">
    <GridAggregates>
        <GridAggregate Field="@nameof(SampleModel.Name)" Aggregate="@GridAggregateType.Count" />
    </GridAggregates>
    <GridColumns>
        <GridColumn Field="@nameof(SampleModel.Name)" />
        <GridColumn Field="@nameof(SampleModel.GroupName)" />
    </GridColumns>
</TelerikGrid>

@code {
    private int OnStateInitCounter1 { get; set; }
    private int OnStateInitCounter2 { get; set; }
    private int OnStateInitCounter3 { get; set; }

    private void OnGridStateInit1(GridStateEventArgs<SampleModel> args)
    {
        ++OnStateInitCounter1;

        args.GridState.GroupDescriptors.Add(new GroupDescriptor
        {
            Member = nameof(SampleModel.GroupName)
        });
    }

    private void OnGridStateInit2(GridStateEventArgs<SampleModel> args)
    {
        ++OnStateInitCounter2;

        args.GridState.GroupDescriptors.Add(new GroupDescriptor
        {
            Member = nameof(SampleModel.GroupName)
        });
    }

    private void OnGridStateInit3(GridStateEventArgs<SampleModel> args)
    {
        ++OnStateInitCounter3;

        args.GridState.GroupDescriptors = new List<GroupDescriptor>();
        // OR
        args.GridState.GroupDescriptors.Clear();

        args.GridState.GroupDescriptors.Add(new GroupDescriptor
        {
            Member = nameof(SampleModel.GroupName)
        });
    }

    private List<SampleModel> GridData { get; set; } = new();

    protected override void OnInitialized()
    {
        for (int i = 1; i <= 4; i++)
        {
            GridData.Add(new SampleModel()
            {
                Id = i,
                Name = $"Name {i}",
                GroupName = $"Group {i % 2 + 1}"
            });
        }
    }

    public class SampleModel
    {
        public int Id { get; set; }
        public string Name { get; set; } = string.Empty;
        public string GroupName { get; set; } = string.Empty;
    }
}

The TelerikGrid never loads any data. the app just hangs. 

I copied the Telerik sample from the online demo. 

 The HTML table loads perfectly.

 Using VS 2019  16.1.0 Preview 2.0.

Acquired Telerik nuget package directly from Telerik feed.

    <TelerikGrid Data=@ViewModel.GetCorePharmacies() Height="300">
        <TelerikGridColumns>
            <TelerikGridColumn Field="ID" Title="NCPDP#" />
            <TelerikGridColumn Field="NPINumber" Title="NPI#" />
            <TelerikGridColumn Field="DBAName" Title="Pharmacy" />
            <TelerikGridColumn Field="StoreNumber" Title="Store#" />
        </TelerikGridColumns>
    </TelerikGrid>

    @*<table class="table">
        <thead>
            <tr>
                <th>NCPDP</th>
                <th>NPI</th>
                <th>DBA Name</th>
                <th>Store#</th>
            </tr>
        </thead>
        <tbody>
            @foreach (var pharmacy in ViewModel.GetCorePharmacies())
            {
                <tr>
                    <td>@pharmacy.ID.ToString()</td>
                    <td>@pharmacy.NPINumber.ToString()</td>
                    <td>@pharmacy.DBAName</td>
                    <td>@pharmacy.StoreNumber</td>
                </tr>
            }
        </tbody>
    </table>*@

Any thoughts. 

<button @onclick="@MyClick">Add item</button>

void MyClick()
{
    MyData.Add(new SampleData() { ID = 46, Name = "from click" });
    StateHasChanged();
}