Space between Header and Body while using ScorllY

Hi Team ,

i am trying to use ScrollY option to have infinite scrolling with CheckBox option. Everything runs fine until i use "scrollY":"400px" datatable start showing space between header and body , please see attached image
Image : https://1drv.ms/i/s!AmJ3g246sggog45LuFRDYPLLGq_0_g
Datatable Initialization is as follows

 $('#tblRoomList').DataTable({
                    select: true,
                    "scrollY": "400px",
                    "paging": false,
                    //  "scrollCollapse": true,
                    data: data,
                    "columns":
                    [
                        { "title": "", "data": "", "defaultContent": "" },
                        { "data": "RoomName", "title": "Name" },
                        { "data": 'StyleName', "title": "Seating Style" },
                        { "data": "Capacity", "title": "Capacity" },
                        { "data": "SetUpTime", "title": " Setup Time" },
                        { "data": "ClubName", "title": "Club Mapped", "defaultContent": "Not Mapped" }
                    ],
                    "columnDefs":
                    [

                        {
                            "targets": [0],
                            "orderable": false,
                            "className": 'select-checkbox'
                        },

                    ],
                    select: {
                        style: 'os'
                    },
                });

using latest version
Please help

Thank you
Dheeraj Kumar