Gantt.sort method does not show arrows in column header

Using gantt.sort method will sort items in gantt grid, but column header does not show arrow, as when user click on header.

I tried to reproduce your issue, but it seems to work correctly to me. The sort icons work properly in the grid when you click on the header.
Please check the example: ;
If you’re using the custom sorting functions: ;
the sorting icons won’t be displayed. But it can be implemented in a custom solution. For this, you can create custom arrows or use this container:
<div class="gantt_sort gantt_asc">
to show sorting icons from gantt.config.sort.
You need to use onDataRender to display your custom icons every time the Gantt is re-rendered. There is an article: ;
You can toggle the CSS classes of the icons when you click on the header with a help of the OnEmptyClick event and gantt.utils module.
Please check the articles: ; ;
Please check the example of how it might be implemented: