Updated to v12.01 and it also upgraded my catalogue. Noticed over last few days when try to import get these messages, example....
The Folders(s) could not be found
Failed to find place for the imported file
Just found similar community report from year ago and was to do with commas in filenames, but these are simply standard Fuji camera file numbers. Also the folders appear perfectly ok on drive, and can access other images in folders.
Welcome to the Lightroom community. I'd love to help you figure this out.
Where do you keep your catalog? On the internal drive or an external drive? Could you please share a screenshot of the import settings you are using? Is the drive connected wirelessly or via a compatible wired connection?
Try changing the port used to a faster input & test if this happens with the specific range of files stored in a specific folder on the drive.