Strange behavior of File method on Chrome Browser

Question

In (one) of my application's controller is defined action/method that allows download file.

public FileResult PDFDownloadA(int attachementid)
{
    string filepath = "";
    byte[] pdfByte;

    SqlConnection conn = new SqlConnection(System.Configuration.ConfigurationManager.
                                            ConnectionStrings["Zalaczniki"].ConnectionString);
    conn.Open();
    using (var sqlquery = new SqlCommand("SELECT DDOKUMENT,DFILENAME from ATTACHEMENTS WHERE ID = @id", conn))
    {
        sqlquery.Parameters.AddWithValue("id", attachementid);
        using (var wynik = sqlquery.ExecuteReader())
        {
            wynik.Read();
            var blob = new Byte[wynik.GetBytes(0, 0, null, 0, int.MaxValue)];
            wynik.GetBytes(0, 0, blob, 0, blob.Length);
            filepath = wynik.GetString(1);
            pdfByte = blob;
        }
    }

    conn.Close();

    return File(pdfByte, "application/pdf", (filepath == "") ? "temp.pdf" : filepath);
}

And problem part:

It works fine when debugging/runnning on local IIS Express - file got its proper name and downloads properly, but on my production server (iis8.5) file dowloads with name (why ?)

"unknown.pdf____________________________________________________________________________________________________________________________________________________________________________________________".

It seems that it is Google-Chrome behawior, on Edge, Firefox it looks better. Chrome is unfortunately in common use in company so it makes problem. Haven't found any solution so far.

Edit: IIS mime types are set in IIS by default : ex: application/pdf

Answer 1

Solved anyway with myself - this happens when application is .net 4.5.2 but server has .net 4.5 only installed. Another functionalities (forms/queries etc) worked before perfect .

Now it works perfect. Maybe it will be usefull for someone. Thanks for everyone that spent some time on this subject.