@dc42 Update, I saw your post about a similar condition from Dec 2016 about how it might be a bad solder connection.
"So the WiFi module isn't responding when the Duet main processor tries to use the programming interface. Looks like you have a hardware fault. Do all the pads of the WiFi module look adequately soldered to the main board? You can ignore the pads at the back of the module because those connections are not used."
I took a look and touched up two of the pads with my soldering iron and the update went through. I really appreciate all the work you have put into this over the years!