I have recently upgraded from 15.10 to 16.04LTS. Since the upgrade, I have still been prompted occasionally to update by 'Software Updater' which had been present in 15.10. Quite a few updates to Ubuntu core have been done this way.
In the last couple of days, when returning from suspend a popup has appeared in the same place as the wifi connected/disconnected information appears. This new popup told me that 'Important OS and application updates are ready..." before disappearing. Yet when I checked with the 'Software Updater' it told me that the software was up to date. Checking with the new 'Ubuntu Software' (update tab) told me that there were updates, so I clicked 'Install'. It didn't tell me what was being installed.
Why is there this different method of checking and why are the two giving different results?
How can I find out what the new Ubuntu Software did install ?
Edit 9th May
Again today the pop-up appeared. The 'Software Updater' showed the machine was up to date. The 'Ubuntu Software' app showed 1 update. On clicking the '1' icon it showed 1 update, namely: ubuntu-drivers-common 1:0.4.17.1. I clicked the 'Install' button and installed it.
I'm none the wiser as to why it is only shown as necessary by 1 app and not the other.