OnInitializedAsync() Issue with Blazor Telerik

Question

Im using Telerik Blazor controls, I am using mt API to return data which works fine when I check it from an API perspective. My web app has issues as it errors as I believe there is no data. To my knowledge this is due to OnInitializedAsync(). Below is my code:

<TelerikScheduler Data="@HolidayPlanners" @bind-Date="@StartDate" @bind-View="@selectedView" Height="100%" Class="Scheduler" OnCreate="@AddAppointment" 
              OnUpdate="@UpdateAppointment" OnDelete="@DeleteAppointment"
              AllowCreate="true" AllowDelete="true" AllowUpdate="true"
              IdField="@(nameof(UvwHolidayPlanner.Pk))"
              StartField="@(nameof(UvwHolidayPlanner.StartDate))"
              EndField="@(nameof(UvwHolidayPlanner.EndDate))"
              TitleField="@(nameof(UvwHolidayPlanner.Title))"
              DescriptionField="@(nameof(UvwHolidayPlanner.Description))"
              IsAllDayField="@(nameof(UvwHolidayPlanner.IsAllDay))"
              RecurrenceRuleField="@(nameof(UvwHolidayPlanner.RecurrenceRule))"
              RecurrenceExceptionsField="@(nameof(UvwHolidayPlanner.RecurrenceExceptions))"
              RecurrenceIdField="@(nameof(UvwHolidayPlanner.RecurrenceFk))">
<SchedulerViews>
    <SchedulerMonthView></SchedulerMonthView>
</SchedulerViews>

@code {

public string _URL = String.Empty;

IEnumerable<UvwHolidayPlanner> HolidayPlanners { get; set; }

DateTime StartDate = DateTime.Now;

SchedulerView selectedView { get; set; } = SchedulerView.Month;

protected override async Task OnInitializedAsync()
{
    _URL = settingsAccessor.AllClientSettings().BaseServiceURI;


    HolidayPlanners = (await http.CreateClient("ClientSettings").GetFromJsonAsync<List<UvwHolidayPlanner>>($"{_URL}/lookup/HolidayPlanner"))
    .OrderBy(t => t.Title)
    .ToList();

    StateHasChanged();

}

//private void LoadData()
//{
    //Appointments = appointmentService.GetAppointments();
//}


void UpdateAppointment(SchedulerUpdateEventArgs args)
{
    //appointmentService.UpdateAppointment((AppointmentDto)args.Item);
    //LoadData();
}

void AddAppointment(SchedulerCreateEventArgs args)
{
    //appointmentService.CreateAppointment((AppointmentDto)args.Item);
    //LoadData();
}

void DeleteAppointment(SchedulerDeleteEventArgs args)
{
    //appointmentService.DeleteAppointment((AppointmentDto)args.Item);
    //LoadData();
}

}

My HolidayPlanners property seems to return null & it errors. Unsure if this is because the UI Components have already initialized.

Below is a message within the 404 error unsure if thats an issue:

ProjectManager.Pages.Pages__Host.<ExecuteAsync>b__15_1() in _Host.cshtml

    <component type="typeof(App)" render-mode="ServerPrerendered" />

I have tried render-mode="Server" & "Static"