The DataSource's property groupPaging: true prevents the Grid's group from expanding if it has a defined groupHeaderColumnTemplate.
Also reproducible in the Core wrapper where an error is thrown: kendo.all.js:8743 Uncaught TypeError: Cannot read property 'hasSubgroups' of undefined
groupPaging is not compatible with the groupHeaderColumnTemplate
groupPaging and the groupHeaderColumnTemplate should be compatible
Kendo UI version: 2021.2.616
Browser: [all]