SSH timeout when running `cap deploy`


I’m trying to get my company to take their first tentative steps into continuous deployment via CircleCI, and am using Capistrano to deploy our develop branch onto our staging server. I’ve generated a new SSH key, and put the public key on our server. I’ve then added the private key to CircleCI via Project Settings > SSH Permissions > Add SSH Key, but when the cap deploy command runs I get a Net::SSH::ConnectionTimeout error.

I’ve tried to debug this by SSHing into the staging server from my own machine using the same private key and it works, but SSHing into the Circle environment, and trying to SSH into the staging server, I get timeout errors. Is there anything I’m missing here?