Can you provide a separate Debug ID that shows you trying to open a file that's missing? It's not clear from the debug output what the file in question is.

And what is the first Debug ID meant to show? It shows that item being successfully uploaded to your WebDAV server.

But re-read the instructions — it has to be for the computer where the problem is. If the file can be successfully opened on that computer, and it's successfully uploading to the server, the problem is on the other computer, and we would need a Debug ID from that computer.

(3)(+0000000): HTTP GET http://********@localhost:8080/zotero/GB5RGCTX.prop succeeded with 200

(3)(+0000001): <properties version="1"><mtime>1474474603481</mtime><hash>19401b879dc57c5bb7c83784ac46aa43</hash></properties>

(3)(+0000001): File mod time matches remote file -- skipping upload

Actually, I misspoke — the debug output shows it checking the modification time stored on the WebDAV server for that file, comparing it to the time of the local file, and skipping the upload because the time is the same.

You can verify this yourself — the mtime in GB5RGCTX.prop on the WebDAV server is 1474474603481, which is September 21, 2016, and that is apparently the same as the file on this computer. So you'll need to check to make sure that the program you're using on the other computer is properly updating the modification time of the file, at which point, when you sync, that mtime should be updated. Once it is, this copy of Zotero should pull down the updated file.

Are you looking in a different directory? That's an old format for that .prop files that hasn't been used in several years.

It might have changed since the debug output (from another sync), or an old version might be cached in Firefox, though I'm pretty sure we override that. But it's just a GET request, so you can check by loading that URL in Firefox.

Can you reset file sync history and provide another Debug ID?

Yeah, it still appears to be getting the other values. If this were a caching issue, I'm not sure why you would see the newer values when you load the URL directly, but I'm not sure what else it would be. You could try clearing the Firefox cache. I've also updated the WebDAV code for Zotero 5.0, which will be released soon, to bypass the cache. A beta version is available now if you want to try that. There's not really any point debugging 4.0 at this point, since there won't be any more 4.0 releases, but we can investigate further if this still happens with 5.0.

File structure is the same in Zotero 5.0