Calls by Week - Filtered by Month
When running the calls by week report, the first and last week often run over the previous and next month. The label shows this, but when you then filter by month it hides the data from the other months. Makes for a very confusing report and it looks like it contains data from a period that it doesn't.
Scott Rixon commented
Also - Running a report for the last day of each month, means the last few days is cut off..