Hi,
According to your description, it seems you meet an issue when using the third-party backup tool to backup the SQL database. Since we are not familiar with Amazon S2 storage, and there's limited information about the issue on Internet, it's recommended to open a case with MS to check if the issue is Windows related. It's also recommended to turn to Amazon S3 community to check if you may get better help.
Below is the link to open a case with MS:
https://support.microsoft.com/en-us/gp/customer-service-phone-numbers
Thanks for your time!
Best Regards,
Anne
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