If you have an SMTP server you want to test, you might try to connect manually using openssl, such as: openssl s_client -connect smtp.example.com:25 -starttls smtp
What is an equivalent way to connect to the Bisq node? What TCP-based service(s) will be listening on port 9999? If we know this, it will be possible to test poor connections to a local node using that tool at 127.0.0.1:9999 and then also to manually test from a command line using tor or torsocks.
This would be a very good, basic, troubleshooting information to have, and would make it possible for advanced users to do more troubleshooting so the devs do not have to troubleshoot simple issues.