Wasabi Maximum Number of Network Connections Exceeded

I have a large volume, about 10TB, with over 15 millions of files. Attempting Duplicacy backup to Wasabi inevitable fails around 15% with the error below. Adjusting threads, chunk size, and/or rate limit has no effect. Is there a way to rate-limit connections Duplicacy makes to Wasabi?

<ErrorResponse xmlns="https://iam.amazonaws.com/doc/2010-05-08/">
    <Error>
        <Type>Sender</Type>
        <Code>ConnectionLimitExceeded</Code>
        <Message>You have exceeded the maximum number of network connections allowed.  Please try again later.</Message>
        <Detail>Your IP address X.X.X.X opened 538 connections in the last minute, but is only allowed 250 connections per minute.</Detail>
    </Error>
</ErrorResponse>

Does it happen with 1 thread even?