I’ve seen this too, although lately I’ve been manually updating before it has a chance to pop up since I’m running 16.04 
I think it is what was described in this post, too: Software Updater notification behavior
I’ve seen this too, although lately I’ve been manually updating before it has a chance to pop up since I’m running 16.04
I think it is what was described in this post, too: Software Updater notification behavior