This problem started coming up on mine. I normally shut it off at night for about 2-3 hours and then it restarts again in the morning but somehow, of late, with my TP Link Decos (M4R and E4R satellites) and the Mi Box (it''s not an S but like Mi Box 3 from 2017!), it will show that it's connected to the WiFi but have no internet.

I restart the Mi Box, forget the Wifi, add it back and it still doesn't work. I even tried to switch the Mi Box with another one that I have (also from 2017) and using the same HDMI and power cable, it will show it's connected to WiFi but no internet.

It's a Panasonic Plasma TV.

No problems. The only new thing I did was probably add the main router but it was fine because the problem only started happening in the last 2-3 weeks.

I have to restart the mesh then it is OK - my guess is that Mi Box Wifi module and the mesh router doesn't want to play nice anymore after the numerous daily restarts that I make the Mi Box 3 go through. I have now just set it to be on all the time and I think it should work but... I bought the Mi Box S 3rd gen y'day. Hopefully, this will solve the problem.

Actually, the problem may have only started when I subscribed to Youtube Premium two weeks ago. Prior to that, I never really had this problem.