I have a well working wifi AP - actually a number of them. They are just fine themselves. Other ios, mac, windows etc devices auto-connect just fine to it.
I also have Xiaomi mi5 with MIUI 10 Android 8. I have a bunch of them. Even after a factory reset, network reset, ensuring auto-connect is on - it does not re-connect to filtered wifi when it is restarted or when it comes back from out of range distance.
Device says "connected, no internet" on first connection or manual connections after. DHCP is all ok, gets IP. network communication works.
I do understand that it says "no internet" because it tried to test with google servers and it failed. They are filtered here, and no i'm not in China. But the logic of "no google server"="no internet" is not correct. I am assuming that this is the reason it decides not to connect. But I am not sure. And also other android 7 devices don't have this issue.
I ran out of ideas. Any clues on how to make this work?