My 16.04 LTS system is configured with two users: me and a (non-admin) friend. After a recent neighborhood power outage, my user logs out before I can do anything. That is, I get the login (password) prompt and supply the correct password. Screen clears, top bar (indicator) appears with expected icons, unity launcher(?) bar appears with correct icons and hides. Then there's a "flash" (screen goes white for an instant then back to normal), then back to login screen. Once the top bar is visible, I can pull down menus etc, but don't have time for anything actually happen (e.g., if I select Thunderbird).
The other user logs in just fine. Guest session logs in just fine. I can log in to terminal (Ctrl-Alt-F1) as me just fine (as well as su to me from other logins). If I try to switch to me from other user or guest, it's the same as logging in normally (as described above).