Hello Peter,

Thank you for reporting this problem.

The described issue is not expected and we are not aware of such problem. Here are some suggestions which might help in troubleshooting:

1. Ensure that the DataSource of the main page grid (other UserControl grids seem fine) has its DataSource property defined only within the NeedDataSource event handler:
https://www.telerik.com/support/kb/aspnet-ajax/grid/details/how-to-bind-radgrid-properly-on-server-side

2. Check whether there is RadAjax, RadAjaxPanel or UpdatePanel in the MasterPage.master file and temporarily remove it:
https://www.telerik.com/support/kb/aspnet-ajax/ajaxmanager/details/get-more-descriptive-errors-by-disabling-ajax

3. In addition, you can also try the steps provided in this post:
https://www.telerik.com/forums/grid-pdf-export-with-strange-characters-in-azure#aM8-OlGXJUusndSAv6epbQ

If the issue remains after all these suggestions, let me know so I proceed with creating a sample resembling your original project.

Regards,
Eyup
Progress Telerik