Can't play videos with iOS 15 via AVPlayer

I've integrated my iOS app with Dropbox a few years ago and it had been working well, until iOS 15 dropped.  What i'm doing is requesting the "TEMP" link to the file and providing it to the AVPlayerItem.  Before it would just work, but now it is failing with

Error Domain=AVFoundationErrorDomain Code=-11828 \"Cannot Open\" UserInfo={NSLocalizedFailureReason=This media format is not supported., NSLocalizedDescription=Cannot Open, NSUnderlyingError=0x280597990 {Error Domain=NSOSStatusErrorDomain Code=-12847

 

This is strange, since

• I can take that url and download it from my desktop
• I can take the link and from within the app, download it, and play it locally.  This does not use the AVPlayer to download, more Core Http transport tech
• I can post the file to a local UPNP Server and it plays over HTTP

Trying to figure this out, the file is accessible, but won't stream with AVPlayer (The Class, not the App).  Maybe it is some header being sent by dropbox?  I have a webserver proxy I used for playing content from a Flash Drive, so I might be able to work around the issue, but it would be nice to directly play the file.