EDIT: I am leaving this here in case somebody else looks for it. I shut down and restarted the Duet after a while and the upgrade to 3.2.2 seems to have worked, the only problem being that I didn't get a confirmation of the upgrade; the screen just kept showing the "Please wait..." message.
Yesterday I upgraded my Duet 2 WiFi from 2.x to 3.0.0 firmware by uploading through the web UI, which worked fine. I then wanted to proceed to 3.1.1, but the installation through the web UI kept hanging at the "Please wait while updates are being installed" message.
After a while (> 15 minutes) I shut down the Duet. I was able to get back to a usable state with firmware 3.0.0, including working WiFi, by following fallback procedure #1 from the documentation.
Today I decided to give it another try with 3.2.2. I again uploaded through the web UI, and it hangs again at the "Please wait while..." message.
What could I do to debug this? I could roll back to 3.0.0, but at some point I'd like to keep up with firmware updates, obviously.
PS. The Duet 2 Wifi is wired up inside the printer with 6 steppers and a Duex 2 connected. I am doing the upgrade on USB power only, no Vin.