This may be related to the reports of "hangs" and such, and I don't know how to characterize what I'm seeing any better than random chaos...
7.3.1 would do bizarre things when the system was left alone - say for overnight. There are other topics for that, and I'd learned NEVER to leave Lightroom running when I was going to be away from the system for any extended period. This APPEARS to be something else.
System is Windows 10 Pro, 5820 running at 4.4 GHz, 32GB of DDR4 memory, O/S, temp files, cache, and catalog on 1TB SSD. Images on 6TB,7200 rpm HDDs.
Upgraded to 7.4 a couple days ago. I've been processing images from the D850, nothing interesting or unusual, just normal, ordinary Nikon RAW images.
At what appear to be random points - not related to a specific thing I'm doing - Lightroom stops responding, takes about 15% of the CPU and around 13-15 GB of memory, and churns. As near as I can tell, there's NO disk activity to ANY disk - not the images, not the catalog, nothing. But, since Lightroom is shown as "not responding" in the task manager, I'm not sure if there really isn't any disk activity or if the system just can SHOW the activity 'cause it's churning.
On the screen, I'll get a white screen with just the "Lightroom" header, then sometimes a black band with what appears to be the view information that's normally displayed on a loupe image. Clicking on the End task (the red X in the upper right) 'causes the screen to change display, quickly flashing other partial lightroom bits like VERY large pieces of what appear to be the file menu, and other unidentifiable things. If I try to go into Task manager, that window will alternate with a Lightroom window quickly and indefinitely. Needless to say, there weren't going to be any screen captures while all this was going on.
It's extremely difficult to kill Lightroom when it's doing this. SOMETIMES I can go down to the launch bar and tell it to "Close Window", but the popup that says "Program is not responding" ALSO starts alternating with the Lightroom window, making it extremely difficult to tell it to end the program.
During all this, the mouse is extremely unresponsive, increasing the difficulty in attempting to kill Lightroom. SOMETIMES, I'm eventually able to select the Lightroom instance in the Task Manager and End it, but not always.
In at least ONE case last night, there was NO visible Lightroom instance in Task Manager, but the screen continued to alternate between Lightroom and the Task Manager. With no instance of Lightroom in the Task Manager, and no ability to Close the Lightroom instance from the launch bar, I eventually had to crash the system as I couldn't even do a clean shutdown.
It doesn't appear to be related to doing a specific task. On one occasion I'd selected a group of images and told Lightroom to write the metadata to the disk. On another I told Lightroom to export a jpeg from a raw image. On another I attempted to go from Library to Develop... There were several other occurrences.
After having to reboot a couple times yesterday and crash the system twice, as well as ending the Lightroom task several other times. I reinstalled 7.3.1 and I'm currently using that. LR has been up and performing "normal" editing, culling, importing, and so on for the last couple hours without the behavior I was seeing since the upgrade to 7.4.
I have no idea if this is the same thing other's are seeing or if it's another "unique" thing that will get blamed on something other than Lightroom, but 7.3.1 does not APPEAR to be doing the same thing at the moment.