Recently, I’ve been having tons of problems when using FTP at home. I have a Macbook Pro, an Airport Extreme and use Cyberduck to access my remote FTP servers.
It appears that the latest firmware (7.6.x) for the Airport Extreme has issues with FTP connections. In my case, the router would randomly crash while using FTP.
The solution to this, as suggested by a friendly user on the official Apple forum, is to go with SFTP whenever possible. This seems to have solved the problem completely for me, and it even seems faster to top it off.