Bit more info - GPU processing is turned off, but makes no difference.
Please state the exact version NUMBER of Lightroom. We need the NUMBER and not words like "up-to-date" because often people tell us "up-to-date" when it turns out they are not up-to-date.
The only way it is to hard reset my machine.
Does this mean your computer is crashing, or just Lightroom is crashing?
Thanks for the quick response... and apologies for my vagueness.
The computer freezes. Both displays are "on" but curser won't move and keyboard is unresponsive (so I can't alt/tab to another app, or start task manager to close Lr down). It is always about 5 minutes into a Lr session. Disc starts thrashing and everything freezes within a couple of seconds. It doesn't do it with any other app or if Lr isn't running.
I have restored my catalogue from a previous back-up at a time when things were running OK but still errors in the same way.
Well, you say nothing has changed, and yet this has all the symptoms of a hardware malfunction somewhere or bad/corrupted driver (video driver or motherboard driver), that's what has changed. You ought to run diagnostics on your hardware, and re-install all drivers.
I have done some testing. This image is Lr memory use while I am carrying out a 3 minute edit of a RAW file
If I hadn't exited Lr, memory use would continue to rise to 100% and then my machine would lock up. I repeated this test 5 times.
This image is me carrying out exactly the same workflow on the same image but WITH SYNC TO LIGHTROOM CC TURNED OFF.
I have run this test comparison 5 times and every time, if sync to Lightroom CC is turned ON, Lr doesn't release memory and after 5 minutes it crashes and takes my machine with it. Every time I run Lr with sync turned OFF, memory is flatlined. So - while this give some respite, it is only a workaround. I have sent this info to Adobe to get their views on if there is a permanent solution.
What you are describing sounds very similar to a recent problem with a client’s Lr on a Mac. Diagnostics at the Apple store failed the mother board.
Do you have a Current Time Machine backup?
Do you have Apple Care?
Have you tried Disk Repair in Disk Utlitlies?
I'm running a Windows machine, not a Mac.
I've run a range of h/w tests and all are coming back 100% OK.
I am putting this down to a bug in Lightroom rather than anything wrong with my machine given the last set of tests that I did with and without synching turned on. I have done more tests and they are coming back consistently the same - synching with Lightroom CC causes memory not to be released for some reason.
I need to test this on another machine, which I will do later tonight, to see if it fails there too.
Sounds like a bug with the Syncing to CC indeed. That wouldn't be surprising as that part of Classic is quite buggy in my experience.