I had the report html output trouble on report retrieving 32000 lines. The query ran fast but the output into web browser was very slow. In my case I had to activate “Interactive Paging” to allow user to see first page and be able to generate Excel file. The pros of this solution is that first page appears fast and user can generate export to Excel or PDF, the cons is that user can scroll only current page. If user wants to see more content he\she must use navigation buttons above the grid. In my case user accepted this behavior because the export to Excel was more important.
To activate “Interactive Paging” you must click on the free area in the report pane and change property “InteractiveSize”\ “Height” on the report level in Properties pane. Set this property to different from 0. I set to 8.5 inches in my case. Also ensure that you unchecked “Keep together on one page if possible” property on the Tablix level (right click on the Tablix, then “Tablix Properties”, then “General”\ “Page Break Options”).