I work on the Applitools technical support team. I understand that you're running into an issue with downloading the diff images when using the TestResultsHandler class in Java.
It is tough to say exactly what the issue is that you're experiencing without seeing the error messages as well as your code. In any case, here is an example of the TestResultsHandler usage.
Alternatively, you can also use the Eyes Utilities JAR which also provides the capability of downloading the differences.
Lastly, if you're still running into issues, please feel free to reach out to us directly by opening a ticket via this web form.