# get to a cleaner state
sudo apt install ppa-purge
sudo apt remove unity8-desktop-session unity8-desktop-session-mir
sudo apt-get autoremove
sudo ppa-purge ppa:ci-train-ppa-service/stable-phone-overlay

# reinstall
sudo add-apt-repository ppa:ci-train-ppa-service/stable-phone-overlay
sudo apt update
sudo apt install unity8-desktop-session