Dark display

[m654321]

I don't think this is hardware related.  As I stated, I can go to a month old restore point and things work fine, just like they did last week.  The machines I'm talking about are business class laptops.  So the hardware used is very common.  If this were hardware related, I think it would have been an issue from the moment I installed LL 3.x. 
In my opinion, this is software related, and my hunch is it is due to an upstream upgrade, perhaps with the kernel.

I'm no expert on this, but sometimes with newer kernels, or kernel upgrades, older hardware doesn't always appear to be supported: therefore a kernel update/upgrade could cause a malfunction where there was none previously.

This very problem presented itself, when I recently installed PCLinuxOS on a 10-year-old Toshiba Satellite A300. Instead of  a 'dark screen' issue it was an ACPI BIOS error bug, whenever the laptop booted with the 4.11 kernel that came pre-packaged with the PCLinuxOS version being used.  However, Toshiba is supported by older kernel versions and kernel 4.4 did the trick.

So clearly, just taking the Toshiba issue above as an example, both the software (kernel version) and the hardware (age, make/model or type) are both important. So in light of this, maybe it's unhelpful to consider the issue as one of just  "hardware" on the one hand [TC] or  "software" on the other [torreydale], as there seems to be hardware x software (kernel) interaction.

Though your laptops are business class, how old are they? It does seem strange that you were fine with kernel upgrade version #119, but not now, one month later, with #120. Maybe, in time, all machines hit a threshold with software (kernel) compatibility ... 

Excuse the ramble, torreydale & TC  - at this point I feel I'm just "shooting the air"