First try this:
sudo apt-get remove mir-client-platform-mesa3 mir-client-platform-mesa2 mir-client-platform-mesa1
and reboot. If that fixes it then it's bug 1526658.
Second wait a full minute on the black screen. If it gives up and returns to to a (broken) login screen after 30 seconds then it's bug 1536662.
First try this: platform- mesa3 mir-client- platform- mesa2 mir-client- platform- mesa1
sudo apt-get remove mir-client-
and reboot. If that fixes it then it's bug 1526658.
Second wait a full minute on the black screen. If it gives up and returns to to a (broken) login screen after 30 seconds then it's bug 1536662.