This page covers problems with data syncing. For problems with file syncing, see Files Not Syncing.

In Zotero libraries, all existing items are shown in either the library root or the trash. Make sure you're not looking in a collection that contains only some of your items. If you don't see the left pane in the Zotero desktop app, click the bar at the left edge of the window to show it, or go to View → Layout and make sure Collections Pane is checked. If you don't see your collections listed in the left-hand pane, make sure the library is expanded by clicking the arrow or plus sign next to the library. If you see different number of items in a collection, make sure you're not just using a different setting for View → Show Items from Subcollections.

If you're sure you're looking in the right place, check to see whether the data in question has synced to the online library on this site. If you don't see the data in the online library, the problem is on the device where the data originated, and any other device is irrelevant. If the data appears in the online library, the problem is solely on the device where you don't see the data. If the problematic device is a computer, check the sync icon in the Zotero app. If it's still spinning, the sync process hasn't yet completed. Hover over the sync icon to see the current status.

If you see a red error icon to the left of the sync icon (desktop app) or an error in the bottom left (iOS), an error has occurred during the sync. Click the icon or tap the message to view the error. It may give you enough information to fix the problem yourself, or you can post to the Zotero Forums for further assistance. Be sure to include the message you're receiving and a Report ID in your forum post.

In the Sync pane pane of the settings in the Zotero desktop app, click “Choose Libraries…” and make sure that the library you're trying to sync has a checkmark next to it. If not, click in the Sync column to enable syncing for that library. All libraries are set to sync by default.

Check the Sync pane of the app settings to make sure you're syncing with the same account you're using to log in to zotero.org and on each of your devices. If the problem is with a group, make sure the account is a member of that group on zotero.org.

If you're still having trouble, post to the Zotero Forums (in your existing thread, if you have one) with a Debug ID for the first sync after making a change that doesn't sync (e.g., making a change to an item in the online library that doesn't appear in Zotero, or vice versa), along with a description of what's not transferring, including the zotero.org URL after selecting the item in the online library if it appears there. Start debug output logging before making the change and keep it going until the sync has ended.