In the previous LTS version (14.04) this issue didn't occur. I switched to Ubuntu GNOME because of this issue, the unlock screen works correctly now. I hope this gives you more information for diagnosing the problem.
In the previous LTS version (14.04) this issue didn't occur.
I switched to Ubuntu GNOME because of this issue, the unlock screen works correctly now. I hope this gives you more information for diagnosing the problem.