And I have no idea where to start. I've never had this issue but suddenly more recent files are missing from their folders. How could I start to problem solve this? Thanks.
Presumably you mean PDFs ? Does Zotero show an error message when you try to open one of those PDFs ? What exactly does one of those error messages say ?
"Aren't there" doesn't give us anything to go on to advise on your issue. You can refer to https://www.zotero.org/support/kb/files_not_syncing . But we would need more information on what you're actually seeing in Zotero - like error messages - to advise further.
Unfortunately there’s no error message. It’s just as if the clock was turned back and I never had added files to my library over the past 2-3 weeks. Is there a way to access past versions of my library? I’ve been using Zotero for years now and this has never happened. It’s as if my library synced to some previous version.
If you're saying that the parent items *and* "stored" PDFs are no longer on the local computer where you added them, there is no obvious reason why that would happen (if you're talking about a *different* computer, the reason could be that they never synced to that computer from the one where they were added). Other possibilities would include having used a different account or profile when you added the recent files.
The most obvious way to restore from a previous version of your database and PDF file storage would be from your own backups (which everyone should have created themselves). Zotero keeps several past copies of your database on your local computer but they only go back to the last several sessions, and they don't include PDFs. https://www.zotero.org/support/zotero_data#restoring_your_zotero_data_from_a_backup
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I will check the link you sent.
https://www.zotero.org/support/attaching_files#linked_files
If you're saying that the parent items *and* "stored" PDFs are no longer on the local computer where you added them, there is no obvious reason why that would happen (if you're talking about a *different* computer, the reason could be that they never synced to that computer from the one where they were added). Other possibilities would include having used a different account or profile when you added the recent files.
The most obvious way to restore from a previous version of your database and PDF file storage would be from your own backups (which everyone should have created themselves). Zotero keeps several past copies of your database on your local computer but they only go back to the last several sessions, and they don't include PDFs.
https://www.zotero.org/support/zotero_data#restoring_your_zotero_data_from_a_backup