Read the statement by Michael Teeuw here.
Slow SSH & SFTP
Has anyone experienced extremely slow connections over wifi using SSH or SFTP? I have my mirror up on the wall now and last night I tried to ssh in via terminal on a mac and took forever to bring up the command line. As well I tried to use Filezilla to SFTP into my mirror and it just hangs on the connecting to 192.168… I have another PI on my system (connected via ethernet cable though) and I have no problem getting into that one.
Me also have you fix It?
@elblogbruno yeah try using the pi’s ipv6 IP to log in. That fixed things for me.
suffered the same problem and found this:
it solved my extreme unstable SSH connection problem