After recent firmware update connectivity between my smartphone and mi band was lost.Well, it worked for short time after I restarted bluetooth, but lost afterwards.
For steps counting and alarm clock functionality this is not a big deal. But I configured mi band to vibrate for important notifications and rather quickly found that this is useful feature.
When connection lost notifications obviously this does not work.
Un-pair/re-pair band with a phone did not help me here.
But, restarting of smartphone - did.
I do not why, but I do not care - now it works again.
So, if you discover connectivity problems after mi band firmware update, phone restart could be a solution.
Or, probably, you can just update your old mi band to the new one?