Comment 11 for bug 1799319

I just encountered this exact same scenario running Ubuntu Mate 19.04. Software Updater believes all updates have been applied. I get the pop-up saying 19.10 is available, I click the Upgrade button, and the dialog disappears and nothing happens. Again, I drop to a command prompt:

root@ubuntu64:~# do-release-upgrade
Checking for a new Ubuntu release
Please install all available updates for your release before upgrading.

root@ubuntu64:~# apt-get upgrade (following update)
The following packages were automatically installed and are no longer required:
  liblldb-8 llvm-8 llvm-8-dev llvm-8-runtime
Use 'apt autoremove' to remove them.
The following packages have been kept back:
  lldb
The following packages will be upgraded:
  gnome-shell gnome-shell-common

root@ubuntu64:~# do-release-upgrade
Checking for a new Ubuntu release
Please install all available updates for your release before upgrading.

root@ubuntu64:~# apt-get purge lldb
Removing lldb (1:7.0-43ubuntu1) ...

And now do-release-upgrade is proceeding.