I have a lot of catalogs, mostly with the catalog, previews and photos on USB drives. Since the most recent upgrade to LrC (v10), I'm constantly having LR crash with the error saying Lightroom encountered an error reading from its preview cache and needs to quit. I have tried deleting the preview cache folder but the errors still happen as preview files are generated. The only catalogs that I don't have a problem with are on my C: drive. I've been using LR for a long time through multiple updates and never had a problem like this. Some catalogs have a few thousand photos other have in excess of 50,000. There are six different USB drives, so it isn't like one just went bad.
Are you saying that you have catalog files on each of 6 drives, and the same thing is happening with catalogs on each drive? Or are the photos spread over six drives, with the catalogs on one drive?
There are catalogs on different external USB drives. The problems are not confined to just one drive. I think I've had the issue on all six drives but, if not all, certainly most.
External USB drives. Several having issues, So how are they plugged in?
Some possible issues:
If Windows OS, are the USB ports/drives set to not go into power saving? LrC hates Drives being turned off.
Are you having issues with USB ports?
Are you having issues with USB controller(s)
Do you have a driver issue with USB controller or drives?
Not using a hub? Hubs may have issues providing power to drives.
Conflict USB vs a device?
Windows 10. Nothing has changed with the USB drives. This all worked fine with all prior LR versions. The drives are all connected to the same powered hub. I tried running LR as administrator and had more success but still crashing. In one of my catalogs, I had deleted the preview folder, so I tried to generate new previews of just one folder with about 150 photos. It got about 80% done and then the preview cache error happened.
Have you considered resetting the preference file?
The preference file can get corrupted leading to odd behavior. The preference file survives updates, upgrades, and re-installs. This is not to say restoring preference settings to defaults, but to actually delete the file (LrC will create a new one upon launch). Some settings in preferences will reset to defaults as a side effect.
Update: If I plug a USB drive directly into my computer, it doesn't seem to crash. However, if it is plugged into a USB or Thunderbolt 3 hub, it crashes - sometimes right away and sometimes after doing a little work. I bought a Thunderbolt 3 SSD external drive and that seems to be working fine plugged into he TB3 hub. I think what I'll do is copy all of my catalog files and previews to this TB3 drive and leave the photos on the USB drives. It seems like that workaround will work. But something definitely changed with this LR upgrade that it is no longer tolerant of delays that might be caused by these other devices in the way.
Update: I spoke with Adobe Support. It was a very unsatisfying experience. The guy basically said that what I want to do isn't supported, that Adobe products to not work on external drives. This is silly for two reasons. One, I have 3TB worth of just catalog and preview files while my C: drive is just 1TB. The other is I've been running catalogs off external USB drives without a hitch since LR v 2.
The guy basically said that what I want to do isn't supported, that Adobe products to not work on external drives.
Well, that particular Adobe Help Staff member is incompetent.
Another update. I've had success so far making a change in Windows 10. I changed the USB drive from the setting that allows quick removal to 'better performance' and thus far I haven't had a crash. What I tried was based on this article https://www.howtogeek.com/410353/how-to-optimize-usb-storage-for-better-performance-on-windows-10/ Now, this was a Windows change from October 2018, so I still believe Adobe changed something that this started with the most recent release, but hoopefully this will do the trick.
I've had the same issue (although I'm just running my LR Catalog with my RAWs on a single external SSD) and the problem still exists. I followed the link you provided (I've done that). So far for me, I've been able to replicate this problem (not on demand, but it's come up) on two computers now, different drives even (as I originally thought my first external SSD was bad so I bought a new one and copied everything over and created a brand new catalog... same issue). This seems to be a problem with LR itself, as my CaptureOne catalog has no problems running off an external SSD/drive, and yes I've done everything I can think of, even adding a USB 3.1 add-in card to my desktop with the same result (replaced cables, even re-installed Windows again). IT's unfortunately a problem win LR's code that must make it super-sensitive to if the drive disconnects for even a brief period. I've even turned off power-savings options in the DEvice Manager for USB devices. I'm just saying that Adobe needs to fix this, because when it works, it is convenient for those who are on the go a lot (they can simply remove their drive and plug it into another computer that has LR configured to work with the SSD and resume where they left off - no more copying catalogs back and forth).