Comment 2 for bug 1726086

It seems there is a dependency conflict which makes it impossible to have

    lubuntu-desktop

installed together with

    xserver-xorg-core-hwe-16.04

To avoid the problem, I downgraded and (re)installed the non-hwe xserver:

    sudo apt install xserver-xorg-core

This removed xserver-xorg-core-hwe-16.04 (as intended), but also lubuntu-desktop
and a few other things (as a side effect). I then reinstalled these lost packages:

    sudo apt install xorg lubuntu-desktop

[Caution: after the first step (and reboot) the console was nonresponsive, so the second step had do be done from an ssh login.]

I now have a clean system again, but the fact remains that lubuntu-desktop (or one of its dependencies) and xserver-xorg-core-hwe-16.04 seem to be in conflict.