I use an ftp site which apparently requires passive mode. I never even knew this because it is apparently the mac default. So recently (around feb 15 or so?) I log in to upload a file and it just starts throwing 500 errors anytime I try to do anything.

cd /players/amish

550 /players/amish: Permission denied. Please contact your web hosting service provider for assistance.

Eventually I downloaded command line ftp, opened a connection, told it to use PASS mode and did a "cd amish" and it worked fine. So something in a recent high sierra patch appears to be messing around with how cyberduck interacts with the mac os settings.

When I was watching the logs I did see some messages about "sandbox" blocking connections to some port, but I can't reproduce that so I am not sure if it is related.