In https://mail-index.netbsd.org/current-users/2017/09/20/msg032361.html there was a discussion about effectiveness of the "High Performance Networking" patch to OpenSSH that we keep in our tree.
Details about the HPN patch can be found at: https://www.psc.edu/hpn-ssh-home/hpn-ssh-faq/ This led finally to the decision to disable the HPN mode by default by setting the Option HPNDisabled to yes in /etc/ssh/sshd_config for netbsd-10. I have now committed part of the latest version of the HPN changes that handle TCP window auto-scaling, which avoids the issue we saw in the past, at least in the network environments I can test. I'd like to see tests from other people that may help with the decision to re-enable it, or to abandon the HPN changes.