Thank you for contacting us. This issue is connected to the problem that is already reported here: https://github.com/handsontable/handsontable/issues/7017
To make this structure work correctly the dataset and option nestedRows has to be set at the same time. You can check your console as you are probably also getting the error saying that the data structure is incorrect. That’s because the plugin is initialized before the data is set. Unfortunately there are no workarounds at the moment, as even trying to set it using updateSettings will also not work. More details are described in the issue I attached.