I have noticed this bug twice.I don't remember hove I fixed this last time but this time it is not ready to go away.A temperory solution maybe to remove update-notifier from startup applications.
First open a terminal and type.
sudo sed -i 's/NoDisplay=true/NoDisplay=false/g' /etc/xdg/autostart/*.desktop
then open startup applications and uncheck update-notifier.
then again run
sudo sed -i 's/NoDisplay=false/NoDisplay=true/g' /etc/xdg/autostart/*.desktop
I have noticed this bug twice.I don't remember hove I fixed this last time but this time it is not ready to go away.A temperory solution maybe to remove update-notifier from startup applications.
First open a terminal and type. true/NoDisplay= false/g' /etc/xdg/ autostart/ *.desktop
sudo sed -i 's/NoDisplay=
then open startup applications and uncheck update-notifier.
then again run false/NoDisplay =true/g' /etc/xdg/ autostart/ *.desktop
sudo sed -i 's/NoDisplay=
this will do.