Are all of your scheduled reports completing each day? My guess is that one of your scheduled reports is failing, or not finishing, or something is happening at the end of scheduled reports.
The easiest place to get to scheduled reports is from within the reports console itself. They are scheduled using the old task scheduler API, so I don't think they appear in the new task manager anymore (Windows 8: Bring Back the Old Windows 7 Style Task Manager might work).
If you can get to the scheduled task from the reports console or from the task scheduler, you can try adding the /L flag to reports to make it log - then check out the SWLEMReports.log in the reports directory to see if there's any insight there. (You can try using /L manually to see what it does.)