Slickgrid -- Checkbox in Grouped rows not getting checked on front end, but getting the data on the backend

I have implemented grouping in my slickgrid. Each row has a check box and the group also has a checkbox(find below code for same).

The checkboxes are seen at group level. It gets checked and the operations on checking are performed, but the checkbox is not visible as checked on front end.

My rowselection model is -->

assignedgrid.setSelectionModel(new Slick.RowSelectionModel({ selectActiveRow: false }));

If I change the rowselectionmodel to --> CellSelectionModel --> assignedgrid.setSelectionModel(new Slick.CellSelectionModel()); then it gets checked in, but then I'm only able to select one row at a time. Multi selection is not working.

I have tried using groupitemmetadata and syncing the grid as well, but it still doesn't work, and syncGridSelection gives an error.

How I am using syncGridSelection --> assigneddataView.syncGridSelection(assignedgrid, true,true);

I want the checkboxes to be visible as checked on front end, and have multi row selection. Request to kindly help!