Hi-
If the database is using a case sensitive collation, then QueryDB queries (and any other queries made on the database) would be case sensitive. That is a possible cause of the behavior you are encountering.
The collation can be found in SQL Server Management Studio by right-clicking the database and selecting Properties.
Collations with CS in their name are case sensitive. Those with CI are case insensitive.
Can you check the Properties and let us know what you find? Thank you