I experienced the same yesterday. It's a combination of: 1. Stale ~/.Xauthority file 2. Removing ubuntu-desktop-mir doesn't seem to remove the config and it keeps using USC.
Solution: 1. rm ~/.Xauthority 2. sudo apt-get remove unity-system-compositor
The first issue is an old X bug. The second I think is a packaging bug of ubuntu-desktop-mir.
I experienced the same yesterday. It's a combination of:
1. Stale ~/.Xauthority file
2. Removing ubuntu-desktop-mir doesn't seem to remove the config and it keeps using USC.
Solution: compositor
1. rm ~/.Xauthority
2. sudo apt-get remove unity-system-
The first issue is an old X bug. The second I think is a packaging bug of ubuntu-desktop-mir.