I'm new to gnome so please bear with me if this is a noob question. I opened Software Updater and it showed that my device is up to date ( it checked for update 1 min ago). And then I checked for update via terminal and showed 3 upgradable packages. Is this normal? I'm using 19.04
This has been the normal behavior since version 13.04.
In Software Updater only phased updates are available.
Phased Updates are just like regular updates, with the only difference being that they are rolled out to users in gradual stages rather than to everyone at the same time. This staggered release approach is designed to improve the stability of Ubuntu.
By drip-feeding Stable Release Updates (SRUs) to a percentage of Ubuntu users at a time, developers have the chance to monitor any regressions or unforeseen bugs introduced by them.
When issues are detected the update process is stopped to ensure that as few users as possible end up with troublesome updates installed.
But, if all is well after a 6 hour period, then another 10% get the updates and the process repeats.
In terminal all updates are available by the command
sudo apt update && sudo apt upgrade