In one case, the empty report was due to there being no records matching the criteria of the report. It turned out that none of the client's Source records (for Activity Type 'R') have dates in the Program_Date_Time field, which is what the report expects, therefore no date range would work for that Activity Type. Here is a query designed to return all Sources with Activity Type 'R':
SELECT Program_Date_Time, s.*
FROM Sources s
WHERE Activity_Type = 'R'
AND Program_Date_Time IS NOT NULL;
In the same case, the client was only filling out the Break Date/Date values, and not the Program Date/Time that the report expects to be filled with data. To fix this, Support suggested running a datafix to set the Program Date/Time with the Break Date/Date values. The report should then be able to pick up the records if that is done.