A couple thoughts:
- My wife's Model 3 seems to get get stuck sometimes trying to connect to wifi. It looks like it is connected, but my router will show several days of 0 bytes transferred. Rebooting the car clears the problem, and we'll sometimes "magically" get an update right after the reboot. No guarantee but easy enough to try.
- Anecdotally, the cars don't seem to like downloading map updates with a weak wifi connection (2 bars or fewer). I used to only get 1-2 bars in my garage and I ended up with a map download that started and never completed on my car. I finally added an access point in the garage, and the updated completed right away. Not everybody has the option to add an access point in their garage, but it was easy for me the way my house is laid out and actually helped with some other dead areas I had, too.