In this situation, the report has several subreports and previews without a problem with a smaller set of records. However, when the number of records increases, the report loads for a very long time and doesn't generate the report preview.
There might be one subreport that is slowing the report preview process down. Remove each subreport one at a time to identify which subreport is causing the issue. Then split the problem subreport into multiple subreports.