I've also had the same problem. I tested it with a few extensions and the error happened with all of them, so it seems to be an issue with the start of a gnome session. It happens mostly with guest sessions, but I've also seen it happen in normal sessions occasionally.
I've also had the same problem. I tested it with a few extensions and the error happened with all of them, so it seems to be an issue with the start of a gnome session. It happens mostly with guest sessions, but I've also seen it happen in normal sessions occasionally.
I'm also using Ubuntu Gnome 16.04 and lightdm.