recently after one of the updates in the last weeks (not sure which one), I had to discover that LrC lost some of the folders in one of the catalogs. Folders and files are still on the harddrive, not problem.
But using the sync function to get the foldes and files back into the catalog causes LrC to freeze.
The catalog handles about 100K Files and 1.2TB
Bug, Crash or freeze, Import and export, Mac, Problem or error, Sync
Can you please explain in more detail what you are trying to do? Also find out which version of Lightroom you are using (it's under 'Help - System Info') and which version of MacOS you use. You say that Lightroom is missing folders and then that you use the 'Sync function' to try to get them back. I don't understand that. How can you sync a folder that isn't in the catalog in the first place?
Lets make an example: Folder 1 with 3 subfolders, 11, 12, 13. After an update 12 is missing in the catalog. However, the folder is still in the file system, same place as before. So, there was no change in the file/folder structure.
To sync the folder back, I do right click in LrC in the library module on the parent folder 1 and LrC shows me all the files that need to be imported, or the ones that need to be deleted. This way I do sync back the folders, as it follows the folder structure on the harddrive.
Meanwhile it seems that the sync back process did work. However the question remains, why did LrC loose some folder in the cataloge.
Is that folder the latest one? In that case maybe you opened an older catalog. That seems to happen sometimes. I don't see how Lightroom could lose a folder from the catalog. It's a database, so that would mean losing lots of records (each image is a record) just like that, and that is extremely unlikely.
It is not the latest one. And I am quite sure I did open the latest catalog.
It looks like there is a problem with the databse records in deed. There were no error messages when opening the catalog. I did perform the extra integrity check, no issues. Also the backups in the past, including checks for integrity reported no errors.