Hi,
It works for me fine, so it doesn't appear to be a major issue within Azure itself.
You could try downloading the vault credentials file with Azure PowerShell by using the Get-AzureRmBackupVaultCredentials PowerShell cmdlet.
Syntax:
Get-AzureRmBackupVaultCredentials [-TargetLocation] <String> [-Vault] <AzureRMBackupVault>
[-DefaultProfile <IAzureContextContainer>] [<CommonParameters>]
Best regards,
Leon