On my UbuntuStudio partition of this machine, in Synaptic Package Manager, I locked the version of xserver-xorg-video-intel at version 2:2.99.910-0ubuntu1. Then I applied system updates.
On re-booting after applying updates, the system booted normally.
I think this evidence strongly suggests that the xserver-xorg-video-intel package is causing the problem.
But where I have no way of rescueing a system destroyed by this problem, I don't dare run the test where I unlock the version on this package, and apply updates again.
I did another test on this problem.
On my UbuntuStudio partition of this machine, in Synaptic Package Manager, I locked the version of xserver- xorg-video- intel at version 2:2.99. 910-0ubuntu1. Then I applied system updates.
On re-booting after applying updates, the system booted normally.
I think this evidence strongly suggests that the xserver- xorg-video- intel package is causing the problem.
But where I have no way of rescueing a system destroyed by this problem, I don't dare run the test where I unlock the version on this package, and apply updates again.