Hello,
Can you provide me with more information about your sender?
Is it headless (meaning no displays attached)?
It sounds like you have confirmed that you can connect with other remote protocols. Have you verified that the sender is actually running, usually on Linux you will see the sender icon in the top right corner, but not 100% sure where it is when using Ubuntu. I am going to have PM enabled for you, so I can collect some logs. Will reach out in PM as soon as I see it enabled.
Kelly
I am an HP employee.