Had the same issue and the solution was to disable screen lock until it finishes downloading.
However in my case it didn't help a lot 'cause since some months I'm unable to install via the updater and only via fastboot
I have Redmi 3 and been waiting for the update. I installed it yesterday and there are several problems:
The launcher space is narrower - the icons are smaller and there is a big gap from the edges.
Toggles - I have them set separated from the notifications. In the past you could set the grid...