I don't know when this started but I noticed that I was not getting pop up alerts after programs were updated.  I checked in settings and alert-mode was switched off.  I didn't do this and it was working quite recently.  
If I click on it the radio button change for a moment and then back to off.  I never see the blue colour of the on position.
I can just re-install but having settings change by themselves is not good.  Nobody else has access to my laptop.