I'm sorry, but you will unlikely get a help here with general networking questions.
Consider asking at Super User or some other more appropriate site.

Have a strange situation with a single PC that cannot connect to certain SFTP servers. We have tried everything – connecting wired, connecting wirelessly, connecting from inside / outside the office, updating network drivers, deleting / reinstalling WinSCP, creating a new Windows profile, testing with other FTP clients (FileZilla). Nothing works. All other computers we've tested with work, it's just this one computer and its only with certain SFTP servers.

The only difference I have noted with this machine is, when doing a packet trace, it's sending an additional TCP Option (window scale) that other machines aren't. Would this option cause the server to not reply? I tried setting the registry entry below to "0" according to the steps here https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/description-tcp-features#windows-scaling


But the machine still sends the "windows scale" option with SYN packets. I'm not sure that is even the problem, but wanted to put it out to the community to see if anyone had any thoughts?