The clients currently only runs windows firewall. I didn't find any settings particular to Avast in the windows firewall configuration.
I have figured out two work arounds:
1) Disable the webshield for 10 minutes, open putty and connect to the remote server, and once connected to the server via SSH webshield doesn't affect future communication.
2) try Avast main GUI -> web shield -> EXPERT settings -> "...well known browsers only". This is a permanent solution, but probably also reduces Avast web protection.
I run ssh on port 8080 to get around some firewall restrictions in certain enviroments. Know it's non-standard, but work for me