This is not a known issue and it was not reproduced in our testing scenario.
The loading indicator should not cause any flickering during the export:
The loading indicator for the pdf export is specific and can be hidden only with custom CSS rules, but it is not recommended as it may cause additional layout issues.
Could you please send a runnable example reproducing the issue as it may be caused by a custom factor which we are overlooking at this moment.
I will be expecting the example, and will gladly assist.
Telerik by Progress