Basically, open-ssh tries to use the Quality of Service figure for the connection to optimize its performance… and the default assumes a reliability that the Pi Zero W, with its weak WiFi hardware, can’t reliably achieve. That causes long timeouts and loss of connection. Setting IPQoS to “we know it’s a bad connection” makes the protocol less efficient but lets it recover from problems much more quickly.
UseCompression No
Use DNS No
IPQoS 0x00Reboot or restart ssh.
The IPQoS seemed the most effective.
Ref: https://raspberrypi.stackexchange.com/questions/99136/extremely-slow-ssh-on-rpi-zero-w