Restart in Troubleshooting Mode (Help → "Restart in Troubleshooting Mode…”), which temporarily disables all plugins, and if that fixes it, find the plugin that's responsible.
This is the second time you've tried to create a new thread months later with identical content to this one after saying that this was resolved. And now it seems you've gone and edited this thread from a year ago with a new Report ID. It's very hard to help you if you do these things.
1) If you have an existing thread for an issue and the issue isn't resolved, post a new comment to that thread. Don't start a new, identical thread.
2) If you have a genuinely new problem, start a new thread. Don't make a silent edit to the original post that no one will ever see
The new Report ID above shows a different problem from the original problem you reported here, but since you've edited it, let's continue here.
[JavaScript Error: "Error 400 for item 5K7FXTKH-58103 in My Library:
ZoteroObjectUploadError: '5K7FXTKH-58103' is not a valid item key"]
Something has to be very wrong in your library to get this error, and it was almost certainly caused by one of the many plugins you have installed.
The Date Added timestamp is 2025-04-20 19:08:59 GMT. You can convert that to your local time zone and sort the items list by Date Added to find the item in question. The title begins with “Their. Delete that item and empty the trash.
You should figure out what plugin caused this, though. It's also possible other items in your library are affected, so you might get other sync errors after resolving this one.
Upgrade Storage
1) If you have an existing thread for an issue and the issue isn't resolved, post a new comment to that thread. Don't start a new, identical thread.
2) If you have a genuinely new problem, start a new thread. Don't make a silent edit to the original post that no one will ever see
The new Report ID above shows a different problem from the original problem you reported here, but since you've edited it, let's continue here. Something has to be very wrong in your library to get this error, and it was almost certainly caused by one of the many plugins you have installed.
The Date Added timestamp is 2025-04-20 19:08:59 GMT. You can convert that to your local time zone and sort the items list by Date Added to find the item in question. The title begins with
“Their. Delete that item and empty the trash.You should figure out what plugin caused this, though. It's also possible other items in your library are affected, so you might get other sync errors after resolving this one.