Hi Brian,
Thank you for contacting Syncfusion support
In TreeGrid when using the load on demand support the waiting popup will be shown while fetching the date from the server side and it will be closed properly after the data gets fetched. We request you to provide the following details.
1. If you are rendering the TreeGrid control on initial page load otherwise while popup the dialog.
2. If you get any console error in your application.
3. Share the demo video regarding this issue.
Regards,
Punniyamoorthi