Apex Report is not returning enough records.
Selection Criteria lists are built up of available valuesfor each field and the list is headed by e.g. ::: All Contractors :::
If the first character of one of the values contains a character before ': ' in theascii table e.g Space or - then the ::: All Contractors ::: is not displayedbut is available to be selected from the dropdown list.
This will only happen if these characters are accidently typed in the first character of the field.
Re-run Report selecting the ::: ALL Contractor ::: option
Locate the offending record. (you may need to send a Data Alteration Notice)