Last night I set up an old AV500 powerline ethernet to put an access point right next to my car in the garage. The car didn't download anything all night, it was even showing only 3 bars even though it was literally 10 feet away from the AP. This morning I go to work and get back and as soon as I park it starts downloading a LOT, with full signal strength. I looked at my router logs and it downloaded 14.4GB of something in about 30 minutes. I got into the car and the NoA toggle still says to connect to WiFi to download maps, and there is no other software update available.
I don't know what it downloaded! And I don't know if the AP next to the car helped at all. It was definitely connected to the powerline AP last night since it has its own SSID.
Wish the car's interface exposed the download log so we know if something is being tried and failing.