Can't update to 4.2.5 from 4.2.1-1


I’m curious about this statement specially the part 4 not upgrade.

Let me add to this that sudo apt-get upgrade will finish with Reading state information… Done
0 upgraded, 0 newly installed, 0 to remove and 4 not upgraded if you already have installed all latest updates. When you already have installed all updates for your system, sudo apt-get upgrade will not reinstall stuff. If you get a message along the lines of x packages have been kept back, you should

sudo apt-get dist-upgrade

See if that works.

By chance did you try to restart Graylog-server service?

This seams like something is wrong with the repo, by chance do you have Graylog pinned or something?
Do you see the new version of graylog in your repo?
Perhaps this may help

I also found this 4 ya