For PostgreSQL database as Source or Target, ETL Validator provides a Copy option in the test cases like Query Compare and Checksum. If you enable this option and benchmark/run the test case, there is a chance that errors are produced. The Copy command option should be used when your PostgreSQL databases support UTF8 characters. 

When you encounter UTF8 related errors, try to rerun/benchmark the test case by unselecting the Use Copy Command option.