After emailing the developer three days ago, they replied today with with a document containing the settings that were successful for them to download the site I was trying to get. He explained that my search settings could be saved in a similar document so I wouldn't have to reset them every time.
He says that "It looks like the crash that you saw was caused by an invalid URL on another site" and "This problem will be fixed in the next version of SiteSucker."

In the meantime I had kept trying different settings and finally managed to download the site I wanted by limiting the search to the site's server only.

Nice to see that the developer responds to problems and tries to help!