It was worth a shot. Current theory is that the unit somehow lost my license. I'm sending it back to Ted Porter, who has graciously offered to resolve the problem.
There is beta firmware for GS911 WiFi under test at the moment with regard to "loss of licence" affecting a very small No of units
You did not really give detail re the error you had with downloader, only the bit below
"When I press the Continue button on the downloader, I see a message for a few seconds that says it's connecting to the server. Then it throws an empty error message."
I assume you plugged the GS911 into USB, opened the Downloader, it then found the GS911 & showed licence No on screen ? then the dialogue saying connecting to Server followed by the empty error dialogue box ?
With your Win10 System have you turned off the USB power saving ?, there have been problems with that affecting devices not only GS911
Re your comment on pdf, not surprised pdf out of M$ word fails to compress images M$ & Adobe have been less than friendly for years, you may find using PrintScreen & M$ Paint then saving an image file better for showing errors