BBR2 congestion algorithm cripples WinSCP throughput in Windows 11

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BBR2 congestion algorithm cripples WinSCP throughput in Windows 11

Windows 11 supports BBR2 congestion algorithm that can be enabled with the following commands and a reboot:
netsh int tcp set supplemental Template=Internet CongestionProvider=bbr2
netsh int tcp set supplemental Template=Datacenter CongestionProvider=bbr2
netsh int tcp set supplemental Template=Compat CongestionProvider=bbr2
netsh int tcp set supplemental Template=DatacenterCustom CongestionProvider=bbr2
netsh int tcp set supplemental Template=InternetCustom CongestionProvider=bbr2
It works as it should for most applications, but enabling it cripples WinSCP 6.X throughput to an extreme degree. It affects both SSH and SFTP protocols, but only WinSCP is affected. It doesn't cripple throughput when used with PuTTY 0.78+. Any ideas?

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Where can I download BETA or EDGE versions of WinSCP to test if this issue is resolved?

If there is a way to run some debug command to generate useful logs, then please let me know how to do it and to where to submit such logs privately.

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martin
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There's currently nothing to test.
But, please send me an email, so I can send you back a development version of WinSCP for testing. Please include a link back to this topic in your email. Also note in this topic that you have sent the email. Thanks.

You will find my address (if you log in) in my forum profile.

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Uxorious
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Did anybody get anywhere with this.
I just noticed what might be the same issue.
If I just use commandline to scp a file from the server, I get great speeds.
But as soon as I start a 2nd scp at the same time, both of them tank their speeds.

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