Playcustomapp API exception during Create

Does anyone know of any recent changes that would impact uploading custom apps via the the API?

We had it working successfully a few weeks ago, however I tested again today and am consistently getting an exception. I've tried with a couple different developer accounts, and multiple different fresh apk files. I've also updated to the latest version of the API.

Unfortunately the exception does not have very much detail. No exception message or inner exception, and when I view the exception stack trace, it is simply:

at Google.Apis.Upload.ResumableUpload`1.<InitiateSessionAsync>d__25.MoveNext()
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)  
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Google.Apis.Upload.ResumableUpload.<UploadAsync>d__70.MoveNext()

This is a snippet of the C# code. I have tried both Upload and UploadAsync:

    var body = new CustomApp.Data.CustomApp
    {
        Title = SomeTitle,
        LanguageCode = "en-us"
    };

    var devId = SomeValidDeveloperAccountId;

    using (var stream = new MemoryStream(SomeAppData))
    {
        // PlayCustomAppService has been initialized successfully
        var request = PlayCustomAppService.Accounts.CustomApps.Create(body, devId, stream, "*/*");
        request.QuotaUser = SomeID;

        // this always throws an exception now
        var result = await request.UploadAsync();
    }

I've also unsuccessfully experimented sending just the metadata (same exception), as well as POSTing directly to https://www.googleapis.com/upload/playcustomapp/v1/accounts/{account}/customApps (500 return code).

I have also tested using the Google API Explorer while logged into a developer account using the appropriate developer ID. I receive this return payload:

{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "backendError",
    "message": "Backend Error"
   }
  ],
  "code": 500,
  "message": "Backend Error"
 }
}

Thanks in advance for any suggestions.

This was a bug in the Play Console which has now been fixed. If you get errors like this in future (specifically 500s which mean an internal server error) then it is a good idea to contact Google Play Support. This can be done via the help menu (the ? icon) and gives email support (and live chat in some languages/times)