DataGrid Virtualization with DbContext error

Dear Support!

My virtualized DataGrid table freezes with this error:

Error: System.InvalidOperationException: A second operation was started on this context instance before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext.

I have tried to add ServiceLifetime.Transient to the DbContext registration,
I have tried to separat DbContext creation with DbContextFactory but when I scroll down the table stops with this error.

My general repository returns an IQueryable

public IQueryable<TEntity> GetAsync(
    Expression<Func<TEntity, bool>>? filter = null,
    Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>>? orderBy = null,
    string includes = "", int skip = 0, int take = 0)

This is my query handler:

    public async Task<VirtualizeResponse<UgyfelDto>> Handle(GetUgyfelListQuery request, CancellationToken cancellationToken)
    {
        var skip = request.LoadDataArgs?.Skip ?? 0;
        var top = request.LoadDataArgs?.Top ?? 10;
        Int32.TryParse(request.LoadDataArgs?.Filter ?? "", out int filterNumber);
        var filterText = request.LoadDataArgs?.Filter ?? "";

        var items = await _ugyfelRepository.GetAsync(
            x => x.Nev!.StartsWith(filterText) || x.Id == filterNumber || x.TAJ!.StartsWith(filterText) || x.IgSzam!.StartsWith(filterText),
            x => x.OrderBy(y => y.Nev),
            "",
            skip, top)
            .Select(x => new UgyfelDto { Id = x.Id, Nev = x.Nev, SzulDatum = x.SzulDatum, TAJ = x.TAJ, IgSzam = x.IgSzam })
            .ToListAsync();


        var totalSize = await _ugyfelRepository.CountAsync();

        return new VirtualizeResponse<UgyfelDto> { Items = items, TotalSize = totalSize };
    }

And how I call it:

    string? lastfilter;
    async Task LoadData(Radzen.LoadDataArgs args)
    {
        await Task.Yield();

        if (!string.IsNullOrEmpty(args.Filter) && lastfilter != args.Filter)
        {
            args.Skip = 0;
        }

        var data = await Mediator!.Send<VirtualizeResponse<UgyfelDto>>(new GetUgyfelListQuery
        {
            LoadDataArgs = new LoadDataArgs { Skip = args.Skip, Top = args.Top, Filter = args.Filter, OrderBy = args.OrderBy }
        });

        ugyfelek = data.Items;
        count = data.TotalSize;
    }

Can you help me with some advise, please?