Haven't had auto connect do its thing yet. Pretty much every wifi that I have encountered (restaurants, shops, etc.) require a sign in, or at least a check in the box and acknowledgment. Did you figure out what it is connecting to?
Did a little test. Started a YouTube video live stream. (Skynews) while I was on public wifi. Walked home and it connected to LTE and than connected to my home wifi all without stopping the live stream video. Pretty cool.
I remember when phone companies even had trouble handing off voice calls even from one cellular band to another, from 3G to 2G, etc. I read that with Fi, voice calls get handed off from cellular to WiFi without interruption. That's pretty cool. Nice tech.
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