Same laptop that has been running WUs for months on end, now with a Windows update (Windows 10 Home 64-bit), no longer crunches, when the lid closes.

I went through all the power settings, but couldn't find any setting that was wrong.
Even set back the 'lid close - do nothing' to 'sleep' or 'shutdown', and back to 'do nothing', but to no avail.

Was wondering if someone else has experienced the same thing?

I have a Windows 10 laptop running 2004 pro, build 19041.388 - it claims to be fully up-to-date.

I've just tried closing the lid, while monitoring on a remote Manager. It kept running - as it does when I close the lid to keep the light down overnight.

odd.
I can't think of anything else that happened to it.

I can tell that it stops working (or at least, stops working at full speed), when I run HWmonitor.
HWMonitor registers 75C under full load (I have a tiny USB fan mounted on the back, blowing in air in the chassis, as this is a fanless system).
When I open up the laptop again, it registers 35-40C.
It does appear like some WUs have been processed, however, the laptop feels cool, not warm like usual.

Nothing else has happened to it.

I just now (after the incident), updated Boinc to 7.16.7; hoping it'd fix the issue.
Will see tonight, as I'm needing it now for work.

You may have answered your own question - some laptops run very much hotter with the lid down than the lid up, and thus, despite all our attempts to keep them running the thermal management kicks in, over-rules our settings and depending on the laptop either seriously reduces performance or stops working. One thing to remember is that laptops have highly optimised thermal management systems, and the vast majority of these systems rely on the exposed surface of the keyboard to shed some of the heat, and putting the lid down puts what is effectively an insulating layer into the cooling path.

You may have answered your own question - some laptops run very much hotter with the lid down than the lid up, and thus, despite all our attempts to keep them running the thermal management kicks in, over-rules our settings and depending on the laptop either seriously reduces performance or stops working. One thing to remember is that laptops have highly optimised thermal management systems, and the vast majority of these systems rely on the exposed surface of the keyboard to shed some of the heat, and putting the lid down puts what is effectively an insulating layer into the cooling path.

No in the past it would crunch through data at full speed, as the fan cools down the CPU enough, that closing it wouldn't matter.
In the past I did only GPU crunching, now I add CPU to it.

With GPU crunching, adding 1 CPU thread = 60c, plenty cool even with lid closed 60% CPU utilization @~2,2Ghz.
GPU + 2 CPU threads = 75C (just a little thermal throttling going on ~1,8-1,9Ghz down from 2,59 max with CPU only and without GPU)
2 CPU threads + GPU also show 100% CPU utilization in Taskmanager, so I don't add more than that.

75C with lid closed should still not thermal throttle.
Windows may however, lower C-state with the lid on, where as before it would just lower C-state when the laptop went to sleep.
(sleep/hibernation/log off is disabled on my laptop).

It all depends what is getting hot - most laptops have far more thermal sensors than just those in the CPU - the internal power supplies, battery, battery management system and even the display(*) in one case I know of have their own. Any of these exceeding its own limit will either reduce the processor speed or shut the computer down. The fact that at one time a particular computer would run happily at a given (CPU) temperature does not mean that it will do so indefinitely, things wear out, things get dirty, calibration drifts etc.

(*) I found this out when one of mine decided to shut down when I closed the lid (having blanked the screen) and let it continue chuntering through a big FEA - a big chunk of digging later I was told that (and found) there was a thermal sensor in the lid, and if it went outside bounds (hot or cold!) it would shut the system down without too much of a thought as to what was going on. At least I only lost a couple of hours processing out of a hundred hour run.