I have found several posts related to sync issues in the Zotero Forum, but I am not quite sure that any of these can solve my problem. Lately I have noticed that some references in one of my local library subfolders (work computer) were gone, or rather they ended up in the "Unclassified" subfolder - not very useful. The Web Library, and the local library on my home computer, were identical, i.e., empty subfolders, and references that used to be in these subfolders were now in the "Unclassified" subfolder. Fortunately, Time Machine on my home computer allows me to retrieve a previous version of the entire home computer library, with references in the appropriate subfolders. However, after uploading this previous version and allowing sync to proceed, the Web Library version with empty subfolders overwrites the local folders, which end up empty again. Is the solution to replace the online library with the contents of my home computer local library, as per the instructions from https://www.zotero.org/support/kb/sync_reset_options? I am hesitant to proceed, because the backup library on my home computer appears to have some missing subfolders, so whantever local library I use to restore and sync, I might end up losing references, or else they will be misplaced in the not-very-useful "Unclassified" folder. What I would like to do is to merge the two local libraries (work and home computers), with elimination of duplicates, before allowing sync to proceed as usual. Is this doable? Or else do you have a solution?