Can't download gallery files "Could Not Locate this item"

@devyx11  It looks like most or all of your Tray items are missing files.  For reference, this post lists the various file types:

https://www.carls-sims-4-guide.com/forum/index.php?topic=26535.0

As you can see, every type of item includes a file with a .trayitem extension, which many of your clusters of files (grouped by timestamp) are missing.  Those that do include a .trayitem file are still missing something else.

I don't know why these files would have disappeared—maybe you were running a program meant to save space that flagged these files as extraneous and deleted them.  Point is, if you can't find the missing files, then I doubt there's anything you can do to recover the associated library entries.  I once tried to delete one of the files at a time and recreate a dummy version, hoping that the game could still recover enough info for me to place a given lot, and I got nowhere, but you could try if you wanted.  The key would be that the name of the file, the string that comes before the file extension, would need to match exactly.

Hopefully you uploaded at least some of these Library items to the Gallery, in which case you can download them into a clean Tray folder, and they should work fine.  But otherwise, there's unfortunately not much you can do.