Download Diagnostic Report Gives "Internal Server Error"

I'm running RHV 4.1 (EL7.3) and trying to download the Diagnostic Reports. The progress bar run smoothly without any problem when I create the report, but when I click on the "Download Report", it gives "Internal Server Error". I have tried a few times but it always end with the same error message.

Is there any place I can get more clues about the error?