AppStream stopped working in Safari on MacOS

Our AppStream app has recently stopped working in Safari on MacOS. It works fine in Chrome on MacOS and on Windows.

The fleet instance appears to start but the UI hangs while displaying Connecting.

If I put Safari in developer mode and change the user agent to something other than the default Safari one, for instance to impersonate a Chrome or Edge or FireFox Mac browser, then the browser connects to the streamed app.

Is there some new limitation on streaming applications only to Safari on MacOS or is this a bug?