Similar issue on initial loading of the viewer was present in previous versions due to the asynchronous loading of CSS files. Loading all required Telerik Kendo UI CSS files, the viewer's CSS file in the head of the page resolves the issue. Also the fix added in the latest releases of Telerik Reporting should handle the issue without additional settings.
Inspect the page and any external CSS and JS files that may include rules, functionality that hides the DIV of the parameters' area.
Since we are not aware of such problem in the latest releases, we will need a log file by Fiddler and a demo project that illustrates the problem. Include also details about the tested browsers.
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