So, later I found out that the "missing" library moved to "Unfiled Items". I tried to move them by creating a new library folder called "PhD1" because I needed to work. But the problem isn't solved because the original folder had been created over a period of 5 years with sub-folders etc.

Well, I have a screen shot but I am not sure how to "upload it somewhere". I am not this technologically savvy. This is a completely new item that came into my Zotero after I "upgraded" to something else. One says, "My Publications", another "Duplicate items" and then "Unfiled Items" before "Trash". Like I said, although I lost my "PhD Research" collection, it all seemed to have moved into the "Unfiled Items" except that they did not move with all my other sub-folders I have build for over 5 years. There were a total of 2676 items in this "Unfiled Items". I copied and pasted them into a new folder I call "PhD1". When I tried to recopied and re-paste back into the "Unfiled Items" it wouldn't move. Also, I am unable to add new items into my newly created "PhD1" folder. To answer your question, my missing original "PhD Research" collection is also missing from Zotero online. But the new one "PhD1" has been added. Interestingly, the online collection also does not show any of these: "My Publications", "Duplicate items", or "Unfiled Items". I really wish help would be sooner rather than later. But I guess there is no direct helpline for Zotero assistance right?

You can use any free image hosting site to share screenshots.
e.g. on imgur.com you can just paste an image from your clipboard and get a URL you can share, without creating an account. Dropobox or Google Drive are other options.

What Veronica describes just sounds like they accidentally deleted one of their collections -- the Zotero update just co-incidentally happened at the same time.

@Sapphire9993 I'd recommend starting a new discussion -- even similar issues often require quite different troubleshooting and that gets confusing with multiple users.
Note that there is also a Sapphire99933 account and part of your issue may (!) be that you're confusing those two accounts.

@Sapphire9993: Thank you for your support. You did not cause a hysteria. I can see the need to start another forum discussion. Nevertheless, it is important to receive your support which makes me feel that I am not the only in this mess. I can't thank you enough!

However, Zotero MUST be aware of these nightmares. Before I continue, I MUST STRESS @adamsmith and @dstillman: I did not mistakenly delete my collection. To delete an item in Zotero requires at least a right-click plus action. All I remember is saying "yes" to an upgrade while trying to enter a new material into my PhD Research folder.

I noticed that I have the most recent version of Zotero, which is exactly what I downloaded since I have automatic downloads (5.0.33) - https://www.zotero.org/support/5.0_changelog. Zotero has been fixing bugs associated with this most recent version which include disappearance of list items. This is exactly what happened to me. I will emphasize again, the specific library collection I am missing is not deleted. In fact, I have over 5,000 entries in Zotero housed in some 46 separate folders. Only my PhD Research collection was moved to a strange folder call "unfiled" but with no sub-folders. I am not crying but really frustrated that there's no one out here from Zotero on this so-called "open-source" to sort out these problems as efficiently as possible. Hopefully, I'll get my husband to help me sort this out after he gets home today. He's the engineer with far better computer skills than I am.

Otherwise, I'll try to restore an old file from my older mac which still have the original sub-folders attached to the PhD Research one but will be missing at least a year's work.

No, sorry, what you're describing is not a known issue, so there's nothing we'd know to fix or address.

"Unfiled" isn't a strange folder but an automatic collection (which has been around for many years) that holds all items not currently in a collection. What I understand you're seeing is _exactly_ what would happen if you accidentally deleted a collection: the items are still there, but they are in no collection, so they automatically appear in unfiled. I obviously can't prove to you this happened and it's certainly possible something else happened, but I can tell you that this is not an issue that was ever diagnosed (or fixed) with Zotero, be it version 5 or any version before. This can happen by accident relatively easily (arguably too easily) by pressing delete and return on your keyboard with a collection selected.

The fixed issue in 5.0.33 you're referring to was a pure display issue, where the list of items didn't _appear_ in the middle panel when you started the software. They were never actually gone from anywhere (and since the issue is now fixed this wouldn't apply anymore anyway). What Sapphire is describing is also a different issue where items seem to be actually gone, and we'll need more information to see what's going on there, but it's definitely not the same problem (which is why I encouraged them to start a separate discussion).

But to move on towards fixing this -- you don't have any back-ups of your harddisk more recent than a year? Your Zotero library would be on any full harddisk back-up that you've taken recently and it'd be pretty easy to restore from that. E.g. Mac TimeMachine would do this automatically once set up.

OK @adamsmith, obviously I know nothing about what happened! Moving on...I do backups but had serious trouble locating my Zotero backup files. I followed a Zotero weblink to find my Zotero backup but for the life of me I just could not locate it on my external drive. I read sometimes Time Machine does not back-up Zotero. Again, I am ignorant when it comes to technology. Any suggestion on how to find Zotero backup on my external drive? And, yes, I use Time Machine to backup my files every two weeks.

@dstillman: Thank you for the help. But again, your suggestion about what actually happened is not accurate. Sorry. I have been actively working on my PhD and multiple research files for years. As an academic and a professor, it's impossible to not use reference manager to write/teach which is why I have both EndNote and Zotero. I will try the restoration process with some help from my husband. Otherwise, I will spend my entire day trying to figure out simple stuff.

Thank you everyone! As I indicated, my husband, who is way more technologically savvy than me, has sorted out my missing collection. Apparently, he was able to retrieve a backup file from my hard drive, which had my last updated collection. He reinstalled the collection and over-wrote the "damaged" one. So, I have the PhD Research collection back (YAY)! But, interestingly, time machine has not been backing up Zotero. Does anyone have an answer? The essence of backing up is to ensure all my files are stored. Why isn't Zotero backing up on Time Machine? Is there a manual way to do this?

Thanks once again to everyone for the support. I greatly appreciate.

Hello! This is the aforementioned husband. I was able to find a backup sqlite database file that, I am guessing, was automatically created when Zotero was updated to the newer version. Here is what I did to fix the problem:

1) Disconnect from the internet
2) Copy the current (broken) zotero.sqlite to a safe place under a new name
3) Copy the backup database file (zotero.sqlite.77.bak in this case) to zotero.sqlite
4) Open Zotero and verify that the database is the latest one
a) Click the column selector button in the upper right of the list pane and select the "Date Modified" column
b) Sort by the Date Modified column and make sure that the most recent modification is the latest changes to the database
5) Follow the instructions on the Zotero website to properly "Restore to Online Library" Otherwise, syncing with the server will put you back into a broken state
6) Resolve any conflicts during the restore process

Not being a Mac user, I think the reason that Time Machine backups were not helpful is that Time Machine is not version control. I.e., Time Machine only keeps the latest version of any file (on the external drive). Since there was a Time Machine backup after the PHD Research folder went missing, it saved the broken version of the database over top of the latest good version. There is some mention on the web of being able to retrieve previous versions of files from iCloud Time Machine backups, but I did not need to go that far to find out if the zotero.sqlite versions were in iCloud.

It seems like a good idea to take periodic snapshots of the zotero database and supporting files on the local hard disk, and let those snapshots get backed up with Time Machine. That adds a simple (although labor intensive) version control.

If any of that sounds incorrect, please let me know. Thanks!

And yes, the steps you used to restore were exactly right, glad it worked.

I’m not exactly sure what you mean. Time Machine is a versioned backup program. It will keep many versions of files—ordered by date and time—until the storage space allocated to it is full. Then it will start to discard the oldest backups. You can adjust some of this behavior in the Time Machine Options.

In your case, it’s possible that your computer’s hard drive is large enough that one version fills your entire backup drive (or the partition on the drive you’ve allocated to Time Machine). You might also be filling up your drive if you have several large files that change very frequently (such as a virtual machine).

See the section on restoring different versions of a specific file here:
https://support.apple.com/kb/HT204015