We've not been able to reproduce this locally. Can you share whether this happens on all browsers or on specific one? Also are you able to see the loading image if you run the demo reports installed with the Q3 release? Please open the Visual Studio examples, set the web site as starting project, run it, select a long running report (e.g. Report Book) and let us know of the outcome.
If the problem occurs only in your application, then you must have global styles or themes applied on the page - disable them temporary to verify if they are the culprit. If this proves to be the case, make sure that styles/themes do not affect html elements directly, but are applied through the CssClass property to your controls.
the Telerik team
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