The fingerprint sensor seems to conflict with Smart Lock
I've signed up just recently for this appreciation post.
Got Mi4S, the lack of vibration is a bummer, but so far everything else is fine.
I actually had to re-flash the ROM several times until I managed to achieve stable (so far) operation of GApps, otherwise, the services kept crashing not allowing even normal first start-up. Here's the right order:
1) Factory wipe.
2) Flash ROM.
3) Flash Open GApps.
4) Wipe cache and Dalvik cache.
5) Reboot.
The clean install seems to be crucial for GApps. Any subsequent updates should be straightforward, I guess.
But then, in a couple of hours, I somehow managed to break the fingerprint sensor. After several hours of struggle, fiddling and rebooting, I was already going to re-flash again, when I stumbled upon some barely relevant suggestion to 1) disable the Smart Lock function by switching it off in Security > Trusted Agents, and then 2) reboot the phone. Voila, the fingerprint sensor is back online, working as smoothly as it used under MIUI 9. Hope, this helps.