Microsoft.BingAds.CouldNotUploadFileException error

Hi Team,

We are making call to UploadFileAsync method of Microsoft.BingAds.V13.Bulk.BulkServiceManager.
And it works successfully couple of times and the same call without any code changes fails few times and when it fails we are seeing the following exception:

Microsoft.BingAds.CouldNotUploadFileException: Upload File failed. ---> Microsoft.BingAds.CouldNotUploadFileException: Unsuccessful Status Code: Unauthorized; Exception Message: {"TrackingId":"xxxxxxx","RequestId":"xxxxxxxxxxxxx"}
at Microsoft.BingAds.Internal.HttpService.<UploadFileAsync>d__4.MoveNext() in D:\code\BingadsSDK_DotnetCore\src\BingadsSDK_DotnetCore\Internal\HttpService.cs:line 62

As mentioned in the following link: https://video2.skills-academy.com/en-us/advertising/guides/handle-service-errors-exceptions?view=bingads-13
we have also tried by making retry calls to the same method. But in that case also, It is succeeding sometimes, but there is a failure some times.

Could you please help me in getting this fixed.
Thank you very much in advance,
Haritha