It is noticed that Reporting Engine does not send some of the generated reports when attaching PDF option is selected. The issue only occurs on some reports.
The Reporting Engine is designed to attach PDF files up to 20MB. If the generated reports is over 20MB in PDF format, the email will be not sent.
In order to resolve the issue, uncheck the 'PDF' option and select only the 'CSV' option under the 'Output Actions'. Alternatively, modify the Schedule Report to generate a smaller report(e.g. Reduce the time range for the report).