Can't link offline media

If you keep original media in cloud storage, you are entirely a hostage to fortune - as you've discovered.

The only realistic course of events open to you is to see if you can locate the actual files, and download them to a local drive. If you can, you should be able to relink them from there. Rule 1 of using remote cloud storage is never to keep original material on it if it's the only copy there is. Even if the system is vaguely linking to the files, the chances are that they won't download quickly enough for Audition to open them anyway, which may be a part of your problem.

Why does it happen? Because the internet is a far from perfect place. Every time you try to reconnect to your files, it uses a different path to them, depending on all sorts of things. A very large part of all internet traffic is just servers talking to each other to establish optimum paths at any given time. It's a miracle it works at all, and not infrequently it doesn't. And you may find that your file isn't even coming via one single route; all bets are off. But the download protocols for just transferring files are rather more robust in their handshaking than what happens when an app tries to open a file - and that's why having the files available locally for linking is likely to succeed, when doing the opening incorporating a flaky download isn't.